The rise of the Islamic State of Iraq and the Levant (Isis) has been aided by the continuing failure of the US Government to investigate the role of Saudi Arabia in the 9/11 attacks and its support of jihadi movements such as al-Qaeda in the years since, says former Senator Bob Graham, the co-chairman of the official inquiry into 9/11.

Senator Graham, who chaired the Senate Intelligence Committee, said that successive administrations in Washington had turned a blind eye to Saudi support for Sunni extremists. He added: “I believe that the failure to shine a full light on Saudi actions and particularly its involvement in 9/11 has contributed to the Saudi ability to continue to engage in actions that are damaging to the US – and in particular their support for Isis.”

Senator Graham, a distinguished elder statesmen who was twice Democratic governor of Florida before spending 18 years in the US Senate, believes that ignoring what Saudi Arabia was doing and treating it as a reliable American ally contributed to the US intelligence services’ failure to identify Isis as a rising power until after it captured Mosul on 10 June. He says that “one reason I think that our intelligence has been less than stellar” is that not enough attention was given to Saudi Arabia’s fostering of al-Qaeda-type jihadi movements, of which Isis is the most notorious and successful. So far the CIA and other intelligence services have faced little criticism in the US for their apparent failure to foresee the explosive expansion of Isis, which now controls an area larger than Great Britain in northern Iraq and eastern Syria.

Senator Graham’s criticism of the US policy towards Saudi Arabia is important because it comes amidst growing doubts in the US about the wisdom of President Barack Obama’s plan announced on Wednesday to look to the Gulf monarchs as crucial allies in the US campaign to contain and, if possible, push back Isis after its victories in Iraq and Syria during the summer.

Islamic State fighters commandeer an Iraqi forces armoured vehicle in Mosul, Iraq (AP)

Under the plan, Saudi Arabia is to host a special training facility for “moderate” Syrian opposition which is to fight both Isis and the government of President Bashar al-Assad. A problem is that Saudi Arabia dislikes Isis today, whatever its role in its creation, but it gives priority to regime change in Damascus.

Senator Graham thinks it is wise to engage with Saudi Arabia because, despite Saudi denials, he says it has been “a central figure in financing Isis and extremist groups”. But he is cautious about success from the US point of view because of the Saudi monarchy’s long-term alliance with the Wahhabi clergy and its commitment to spread Wahhabism, the intolerant variant of Islam which denounces Shia as heretics and treats women as chattels under male control. The Senator says that Saudi Arabia not only gives support to Sunni communities worldwide “but the most extreme elements among the Sunni”.

In pictures: The rise of Isis Show all 74 1 /74 In pictures: The rise of Isis In pictures: The rise of Isis Isis fighters Fighters of the Islamic State wave the group's flag from a damaged display of a government fighter jet following the battle for the Tabqa air base, in Raqqa, Syria AP In pictures: The rise of Isis Isis fighters Fighters from Islamic State group sit on their tank during a parade in Raqqa, Syria AP In pictures: The rise of Isis Isis fighters Fighters from the Islamic State group pray at the Tabqa air base after capturing it from the Syrian government in Raqqa, Syria AP In pictures: The rise of Isis Isis fighters Fighters from extremist Islamic State group parade in Raqqa, Syria AP In pictures: The rise of Isis Isis kidnapping A video uploaded to social networks shows men in underwear being marched barefoot along a desert road before being allegedly executed by Isis Getty Images In pictures: The rise of Isis Isis kidnapping Haruna Yukawa after his capture by Isis In pictures: The rise of Isis Isis kidnapping Khalinda Sharaf Ajour, a Yazidi, says two of her daughters were captured by Isis militants Washington Post In pictures: The rise of Isis Isis fighters Spokesperson for Isis Vice News via Youtube In pictures: The rise of Isis A pro-Isis leaflet A pro-Isis leaflet handed out on Oxford Street In London Ghaffar Hussain In pictures: The rise of Isis Isis fighters Isis Jihadists burn their passports In pictures: The rise of Isis Isis controls Syrian Aid A man collecting aid administered by Isis in Syria In pictures: The rise of Isis Isis controls Syrian Aid A woman collecting aid administered by Isis in Syria In pictures: The rise of Isis Isis controls Syrian Aid Local civilians queue for aid administered by Isis. Since it declared a caliphate the group has increasingly been delivering services such as healthcare, and distributing aid and free fuel In pictures: The rise of Isis Iraq crisis Iraqi security forces detain men suspected of being militants of the Isis group in Diyala province In pictures: The rise of Isis Iraq crisis Mourners carry the coffin of a Shi'ite volunteer from the brigades of peace, who joined the Iraqi army and was killed during clashes with militants of the Isis group in Samarra, during his funeral in Najaf In pictures: The rise of Isis Iraqi refugees An Iraqi Shiite Turkmen family fleeing the violence in the Iraqi city of Tal Afar, west of Mosul, arrives at a refugee camp on the outskirts of Arbil, in Iraq's Kurdistan region In pictures: The rise of Isis Isis leader Abu Bakr al-Baghdadi A photograph made from a video by the jihadist affiliated group Furqan Media via their twitter account allegedly showing Isis leader Abu Bakr al-Baghdadi delivering a sermon during Friday prayers at a mosque in Mosul. Abu Bakr al-Baghdadi declared an Islamist caliphate in the territory under the group's control in Iraq and Syria In pictures: The rise of Isis Islamic extremists destroying mosques in Iraq Shiite's Al-Qubba Husseiniya mosque explodes in Mosul In pictures: The rise of Isis Islamic extremists destroying mosques in Iraq Smoke and debris go up in the air as Shiite's Al-Qubba Husseiniya mosque explodes in Mosul. Images posted online show that Islamic extremists have destroyed at least 10 ancient shrines and Shiite mosques in territory - the city of Mosul and the town of Tal Afar - they have seized in northern Iraq in recent weeks In pictures: The rise of Isis Islamic extremists destroying mosques in Iraq A bulldozer destroys Sunni's Ahmed al-Rifai shrine and tomb in Mahlabiya district outside of Tal Afar In pictures: The rise of Isis Iraq crisis Iraqi security forces celebrate after clashes with followers of Shiite cleric Mahmoud al-Sarkhi, in front of his home in the Shiite holy city of Karbala, 50 miles (80 kilometers) south of Baghdad In pictures: The rise of Isis Iraq crisis Iraqi security forces arrest a follower of Shiite cleric Mahmoud al-Sarkhi after clashes with his followers in the Shiite holy city of Karbala, 50 miles (80 kilometers) south of Baghdad In pictures: The rise of Isis Iraq crisis Iraqi security forces arrest a follower of Shiite cleric Mahmoud al-Sarkhi at his home after clashes with his followers in the Shiite holy city of Karbala, 50 miles (80 kilometers) south of Baghdad In pictures: The rise of Isis Iraq crisis Iraqi security forces arrest a follower of Shiite cleric Mahmoud al-Sarkhi after clashes with his followers in the Shiite holy city of Karbala, 50 miles (80 kilometers) south of Baghdad In pictures: The rise of Isis Iraq crisis A vehicle burns in front of a home of a follower of Shiite cleric Mahmoud al-Sarkhi after clashes with his followers in the Shiite holy city of Karbala, 50 miles (80 kilometers) south of Baghdad In pictures: The rise of Isis Iraqi refugees An Iraqi woman holds her exhausted son as over 1000 Iraqis who have fled fighting in and around the city of Mosul and Tal Afar wait at a Kurdish checkpoint in the hopes of entering a temporary displacement camp in Khazair In pictures: The rise of Isis Iraqi refugees Displaced Iraqi women hold pots as they queue to receive food during the first day of the Islamic holy month of Ramadan, at an encampment for displaced Iraqis who fled from Mosul and other towns, in the Khazer area outside Irbil, north Iraq In pictures: The rise of Isis Isis fighters in Syria A militant Islamist fighter waving a flag, cheers as he takes part in a military parade along the streets of Syria's northern Raqqa. The fighters held the parade to celebrate their declaration of an Islamic "caliphate" after the group captured territory in neighbouring Iraq In pictures: The rise of Isis Isis fighters in Syria Isis fighters wave flags as they take part in a military parade along the streets of Syria's northern Raqqa province Reuters In pictures: The rise of Isis Isis fighters in Syria Isis fighters travel in a vehicle as they take part in a military parade along the streets of Syria's northern Raqqa province In pictures: The rise of Isis Isis fighters in Syria Fighters from the Isis group during a parade with a missile in Raqqa, Syria. Militants from an al-Qaida splinter group held a military parade in their stronghold in northeastern Syria, displaying U.S.-made Humvees, heavy machine guns, and missiles captured from the Iraqi army for the first time since taking over large parts of the Iraq-Syria border In pictures: The rise of Isis Isis fighters in Syria Isis fighters during a parade in Raqqa, Syria In pictures: The rise of Isis Isis fighters in Syria Fighters from the Isis group during a parade in Raqqa, Syria. Militants from the splinter group held a military parade in their stronghold in northeastern Syria, displaying U.S.-made Humvees, heavy machine guns, and missiles captured from the Iraqi army for the first time since taking over large parts of the Iraq-Syria border In pictures: The rise of Isis Isis fighters in Syria Isis fighters hold a military parade in their stronghold in northeastern Syria In pictures: The rise of Isis Isis fighters in Syria Isis fighters during a parade in Raqqa, Syria In pictures: The rise of Isis Isis fighters in Syria A member loyal to the Isis waves an Isis flag in Raqqa In pictures: The rise of Isis Iraq crisis Iraqi anti-government gunmen from Sunni tribes in the western Anbar province march during a protest in Ramadi, west of Baghdad. The United Nations warned that Iraq is at a "crossroads" and appealed for restraint, as a bloody four-day wave of violence killed 195 people. The violence is the deadliest so far linked to demonstrations that broke out in Sunni areas of the Shiite-majority country more than four months ago, raising fears of a return to all-out sectarian conflict In pictures: The rise of Isis Iraq crisis Iraqi security forces hold up a flag of the Isis group they captured during an operation to regain control of Dallah Abbas north of Baqouba, the capital of Iraq's Diyala province, 35 miles (60 kilometers) northeast of Baghdad In pictures: The rise of Isis Isis fighters in Iraq Isis fighters parade in the northern city of Mosul In pictures: The rise of Isis Iraq crisis Volunteers, who have joined the Iraqi army to fight against the predominantly Sunni militants from the radical Isis group, demonstrate their skills during a graduation ceremony after completing their field training in Najaf In pictures: The rise of Isis Iraq crisis Kurdish Peshmerga troops fire a cannon during clashes with militants of the Isis group in Jalawla, Diyala province In pictures: The rise of Isis Lieutenant General Qassem Atta speaks during a press conference Iraqi Prime Minister's security spokesman, Lieutenant General Qassem Atta speaks during a press conference about the latest military development in Iraq, in the capital Baghdad. Iraqi forces pressed a campaign to retake militant-held Tikrit, clashing with jihadist-led Sunni militants nearby and pounding positions inside the city with air strikes in their biggest counter-offensive so far In pictures: The rise of Isis A police station building destroyed by Isis fighters An exterior view of a police station building destroyed by gunmen in Mosul city, northern Iraq. Iraq's new parliament is expected to convene to start the process of setting up a new government, despite deepening political rifts and an ongoing Islamist-led insurgency. Iraqi President Jalal Talabani issued a decree inviting the new House of Representatives to meet and form a new government In pictures: The rise of Isis Isis fighters in Iraq Smoke billows from an area controlled by the Isis between the Iraqi towns of Naojul and Tuz Khurmatu, both located north of the capital Baghdad, as Iraqi Kurdish Peshmerga forces take part in an operation to repel the Sunni militants In pictures: The rise of Isis Iraqi refugees An elderly Iraqi woman is helped into a temporary displacement camp for Iraqis caught-up in the fighting in and around the city of Mosul in Khazair In pictures: The rise of Isis Iraqi refugees An Iraqi Christian woman fleeing the violence in the village of Qaraqush, about 30 kms east of the northern province of Nineveh, cries upon her arrival at a community center in the Kurdish city of Arbil in Iraq's autonomous Kurdistan region In pictures: The rise of Isis Iraqi refugees An Iraqi woman, who fled with her family from the northern city of Mosul, prays with a copy of the Quran AP In pictures: The rise of Isis Isis fighters in Iraq The body of an Isis militant killed during clashes with Iraqi security forces on the outskirts of the city of Samarra Reuters In pictures: The rise of Isis Iraq crisis Iraqi civilians inspect the damage at a market after an air strike by the Iraqi army in central Mosul EPA In pictures: The rise of Isis Iraq crisis Members of the Al-Abbas brigades, who volunteered to protect the Shiite Muslim holy sites in Karbala against Sunni militants fighting the Baghdad government, parade in the streets of the city AP In pictures: The rise of Isis Iraq crisis Shia tribesmen gather in Baghdad to take up arms against Sunni insurgents marching on the capital. Thousands have volunteered to bolster defences AFP/Getty In pictures: The rise of Isis Iraq crisis A van carrying volunteers joining Iraqi security forces against Jihadist militants. Prime Minister Nuri al-Maliki announced the Iraqi government would arm and equip civilians who volunteered to fight AFP/Getty In pictures: The rise of Isis Iraq Fighters of the Isis group parade in a commandeered Iraqi security forces armored vehicle down a main road at the northern city of Mosul In pictures: The rise of Isis Iraq An Islamist fighter, identified as Abu Muthanna al-Yemeni from Britain (R), speaks in this still image taken undated video shot at an unknown location and uploaded to a social media website. Five Islamist fighters identified as Australian and British nationals have called on Muslims to join the wars in Syria and Iraq, in the new video released by the Isis In pictures: The rise of Isis Iraq Al-Qa’ida inspired militants stand with captured Iraqi Army Humvee at a checkpoint belonging to Iraqi Army outside Beiji refinery some 250 kilometers (155 miles) north of Baghdad. The fighting at Beiji comes as Iraq has asked the U.S. for airstrikes targeting the militants from the Isis group. While U.S. President Barack Obama has not fully ruled out the possibility of launching airstrikes, such action is not imminent in part because intelligence agencies have been unable to identify clear targets on the ground, officials said In pictures: The rise of Isis Iraq Militants attacked Iraq's main oil refinein Baiji as they pressed an offensive that has seen them capture swathes of territory, a manager and a refinery employee said In pictures: The rise of Isis Iraq Militants from the Isis group parading with their weapons in the northern city of Baiji in the in Salaheddin province In pictures: The rise of Isis Iraq A smoke rises after an attack by Isis militants on the country's largest oil refinery in Beiji, some 250 kilometers (155 miles) north of the capital, Baghdad. Iraqi security forces battled insurgents targeting the country's main oil refinery and said they regained partial control of a city near the Syrian border, trying to blunt an offensive by Sunni militants who diplomats fear may have also seized some 100 foreign workers In pictures: The rise of Isis Iraq Militants of the Isis group stand next to captured vehicles left behind by Iraqi security forces at an unknown location in the Salaheddin province. For militant groups, the fight over public perception can be even more important than actual combat, turning military losses into propaganda victories and battlefield successes into powerful tools to build support for the cause In pictures: The rise of Isis Iraq An injured fighter (C) from the Isis group after a battle with Iraqi soldiers at an undisclosed location near the border between Syria and Iraq In pictures: The rise of Isis Iraq Fighters from the Isis aiming at advancing Iraqi troops at an undisclosed location near the border between Syria and Iraq In pictures: The rise of Isis Iraq Fighters from the Isis group taking position at an undisclosed location near the border between Syria and Iraq In pictures: The rise of Isis Iraq Fighters from the Isis group inspecting vehicles of the Iraqi army after they were seized at an undisclosed location near the border between Syria and Iraq In pictures: The rise of Isis Iraq One Iraqi captive, a corporal, is reluctant to say the slogan, and has to be shouted at repeatedly before he obeys Sky News In pictures: The rise of Isis Iraq Iraqi captives held by the extremists Sky News In pictures: The rise of Isis Iraq Iraqi captives held by the extremists Sky News In pictures: The rise of Isis Iraq Militants of the Isis group force captured Iraqi security forces members to the transport In pictures: The rise of Isis Iraq Militants of the Isis group transporting dozens of captured Iraqi security forces members to an unknown location in the Salaheddin province ahead of executing them In pictures: The rise of Isis Iraq A major offensive spearheaded by Isis but also involving supporters of executed dictator Saddam Hussein has overrun all of one province and chunks of three others In pictures: The rise of Isis Iraq Militants of the Isis group executing dozens of captured Iraqi security forces members at an unknown location in the Salaheddin province In pictures: The rise of Isis Iraq Isis militants taking position at a Iraqi border post on the Syrian-Iraqi border between the Iraqi Nineveh province and the Syrian town of Al-Hasakah In pictures: The rise of Isis Iraq Isis rebels show their flag after seizing an army post AFP/Getty Images In pictures: The rise of Isis Iraq Isis militants waving an Islamist flag after the seizure of an Iraqi army checkpoint in Salahuddin Getty Images In pictures: The rise of Isis Iraq Demonstrators chant slogans as they carry al-Qa’ida flags in front of the provincial government headquarters in Mosul, 225 miles (360 kilometers) northwest of Baghdad. In the week since it captured Iraq's second-largest city, Mosul, a Muslim extremist group has tried to win over residents and has stopped short of widely enforcing its strict brand of Islamic law, residents say. Churches remain unharmed and street cleaners are back at work

The Saudi role in the 9/11 attacks on the World Trade Center in 2001 has long been public knowledge since 15 out of 19 of the hijackers were Saudis, and the leader of al-Qaeda, Osama bin Laden, was a member of the Saudi ruling elite. The 9/11 inquiry found that, for financing, al-Qaeda relied on a core group of private donors and charities in Saudi Arabia and the Gulf.

Despite the Saudi connections of the 9/11 conspirators, Saudi Arabia and its citizens were treated with extraordinary leniency in the wake of the attacks. Some 144 individuals, mostly from the Saudi aristocracy, were permitted to fly back to Saudi Arabia within days of the attacks without being questioned by the FBI. The influential Saudi ambassador Prince Bandar bin Sultan was pictured in cheerful conversation with President Bush on the White House balcony a few days after 9/11. Senator Graham recalls that “there were several incidents [in which US officials] were inexplicably solicitous to Saudis”. US officials who went to Saudi Arabia to investigate links to 9/11 found their Saudi counterparts to be persistently obstructive.

Prince Bandar bin Sultan (AFP)

Saudi obstructionism continued during the decade after 9/11: in 2007, Stuart Levey, the Under Secretary of the US Treasury in charge of monitoring and impeding the financing of terrorism, told ABC News that when it came to al-Qaeda, “if I could somehow snap my fingers and cut off the funding from one country, it would be Saudi Arabia”. He added that at that stage not one person identified by the US or the UN as funding terrorism had been prosecuted by the Saudis. Eight years after 9/11, the US Secretary of State, Hillary Clinton, wrote in a cable leaked by WikiLeaks that “Saudi Arabia remains a critical financial support base for al-Qaeda, the Taliban, LeT [Lashkar-e-Taiba in Pakistan] and other terrorist groups.”

As al-Qaeda in Iraq began to reorganise and turn itself into Isis in the years after 2010, politicians and security officials in Baghdad were convinced of the complicity of Saudi Arabia and the other Gulf monarchies in funding jihadis in Iraq. They generally avoided public criticism of these states as allies of the US, but in March 2014 Iraqi Prime Minister Nouri al-Maliki identified Saudi Arabia and Qatar as the two countries “primarily responsible for the sectarian, terrorist and security crisis in Iraq”. He said that Riyadh and Doha were “buying weapons for the benefit of these terrorist organisations”. Mr Maliki had his own share of blame for persecuting the Sunni community in Iraq so it gave support to armed resistance by Isis, but Iraqi leaders all believed that the monarchs of the Gulf were bankrolling Sunni opposition in Iraq and would never accept a Shia-dominated government.

Osama bin Laden (Getty)

The most striking example of Washington’s willingness to protect the Kingdom over complicity in 9/11 is the 28 pages of the official inquiry that were censored and have yet to be published. Senator Graham is not allowed to reveal what is in the chapter that was redacted, but other sources say that they are about connections between Saudi government officials and the 9/11 attacks. Anthony Summers and Robbyn Swan, in their book The Eleventh Day: The Full Story of 9/11, quote a senior American official, who saw the 28 pages before they were excised, apparently on the initiative of President Bush, as saying: “If the 28 pages were to be made public, I have no question that the entire relationship with Saudi Arabia would change overnight.”

Senator Graham has long campaigned to have the 28 pages of the 9/11 inquiry and other documents released. He says, knowing their content, that there is no national security justification for keeping them a secret 13 years after 9/11. He says that some government agencies, notably the FBI, have a motive in keeping information from the public about “their actions and their competence at the time of 9/11”. In Sarasota, Florida, the FBI initially denied having any documents relating to hijackers who were based there but has now handed over 80,000 pages that might be relevant under the Freedom of Information Act, according to Tom Julin, the Miami-based attorney handling the FoI application.

The Twin Towers sparked a series of global events (AP)

Asked why the US government has been so eager since 2001 to cover up for the Saudis, Senator Graham says that one explanation is the long-term US strategic alliance with Saudi Arabia, going back to the Second World War. There is also the close personal relationship between the Bush family and the Kingdom. But what he finds more difficult to explain is why the “policy of covering up Saudi involvement [in 9/11] persisted under the Obama administration”. Though Mr Obama had pledged to the families of the 9/11 victims during the 2008 presidential election campaign to release the 28 censored pages, it has failed to do so six years later.

Senator Graham does not suggest that the Saudis are directly running Isis, but that their support for Sunni extremists in Iraq and Syria opened the door to jihadis including Isis. Similar points were made by Sir Richard Dearlove, the former head of the British Secret Intelligence Service, and MI6, who said in a lecture at the Royal United Services Institute in London in July that the Saudi government is “deeply attracted towards any militancy which effectively challenges Shiadom”. He said that rulers of the Kingdom tended to oppose jihadis at home as enemies of the House of Saud, but promote them abroad in the interests of Saudi foreign policy. Anti-Shi’ism has always been at the centre of the Saudi world view, and he quoted Prince Bandar, the ambassador in Washington at the time of 9/11 and later head of Saudi intelligence, as saying to him: “The time is not far off in the Middle East, Richard, when it will be literally ‘God help the Shia’. More than a billion Sunni have simply had enough of them.”

The jihadi flag of the Islamic State (IS) (AFP)

In allying itself with Saudi Arabia, the US automatically plugs itself into an anti-Shia agenda and limits its ability to monitor and take action against Sunni jihadis who are promoted by Riyadh. In Syria this has led to parts of a jihadi-dominated military opposition being relabelled as “moderate”. President Obama intends to support this group, who scarcely exist on the map, to fight both Isis and the Assad government.

Senator Graham maintains that there is a “dark side” to Saudi Arabia exemplified by 9/11 and its aftermath that the American public need to know about and which has hitherto been concealed. The US and other Western governments have yet to explain why their “war on terror” has so demonstrably failed with the rise of Isis, but tolerance of Saudi complicity in 9/11 will surely be part of the answer.