Iran-backed militias are reportedly being sent to Ramadi by the Iraqi government to fight Isis militants who completed their capture of the city on Sunday.

Government soldiers and civilians were reportedly massacred by extremists as they took control and the army fled. Charred bodies were left littering the city streets as troops clung on to trucks speeding away from the city.

Ramadi is the latest government stronghold to fall to the so-called Islamic State, despite air strikes by a US-led international coalition aiming to stop its advance in Iraq and Syria.

A spokesperson for the governor of Anbar province said that around 500 people, both civilians and Iraqi soldiers, are believed to have been killed in days of battles.

A British Isis fighter who called himself Abu Musa al-Britani was among suicide bombers who led the assault on Friday by using explosive-laden cars to blast their way into a government compound.

Government forces are reported to have fled Ramadi, which lies just 60 miles from Baghdad, despite orders from Prime Minister Haider al-Abadi to hold their positions.

Shia militias known as the Popular Mobilisation (Hashid Shaabi) could be sent in after helping Iraq to recapture Saddam Hussein’s home city of Tikrit from Isis two months ago.

Fall of Ramadi Show all 17 1 /17 Fall of Ramadi Fall of Ramadi Fall of Ramadi A displaced Iraqi Sunni man pushes an elderly woman in a wheelchair on the outskirts of Baghdad. Reuters Fall of Ramadi Fall of Ramadi An Iraqi family, who fled the city of Ramadi after it was seized by Islamic State (IS) group militants, gathers inside a tent at a camp housing displaced families. AFP Fall of Ramadi Fall of Ramadi Displaced Iraqis from Ramadi. AP Fall of Ramadi Fall of Ramadi Iraqi fighters of the Shiite militia Asaib Ahl al-Haq (The League of the Righteous) stand guard outside their headquarters AFP Fall of Ramadi Fall of Ramadi Iraqis fleeing from their hometown of Ramadi walk on a street near the Bzebiz bridge, 65 kilometers (40 miles) west of Baghdad. AP Fall of Ramadi Fall of Ramadi Iraqi Sunni tribal leaders demand Prime Minister Haider al-Abadi to send forces to protect their city and regain Ramadi shortly after Iraqi security forces withdraw from the city. AFP Fall of Ramadi Fall of Ramadi Displaced Iraqis from Ramadi rest before crossing the Bzebiz bridge after spending the night walking towards Baghdad. AP Fall of Ramadi Fall of Ramadi Ramadi, after fighting on Friday, was one of the army’s few strongholds Reuters Fall of Ramadi Fall of Ramadi Iraqi security forces withdraw from the Anbar state capital, Ramadi, in defeat on Sunday, 17 May (AP) AP Fall of Ramadi Fall of Ramadi Iraqis fleeing from their hometown of Ramadi walk on a street near the Bzebiz bridge, 65 kilometers (40 miles) west of Baghdad AP Fall of Ramadi Fall of Ramadi 130,000 remaining inhabitants of Ramadi, an overwhelmingly Sunni city, have fled the fighting (AP) AP Fall of Ramadi Fall of Ramadi Thousands of civilians fled the Isis advance in Ramadi AP Fall of Ramadi Fall of Ramadi Iraq security forces were seen fleeing from Ramadi, the capital of Iraq's Anbar province AP Fall of Ramadi Fall of Ramadi Civilian belongings can be seen in an abandoned truck during fighting in Ramadi Reuters Fall of Ramadi Fall of Ramadi Isis led its renewed assault on Ramadi with suicide car bombs on Friday Reuters Fall of Ramadi Fall of Ramadi The last remaining Iraqi security forces defending their headquarters against Isis in the eastern part of Ramadi on 14 May Reuters Fall of Ramadi Fall of Ramadi Civilians fled Ramadi as Isis advanced earlier in May. Reuters

Using them is a risky move by the government, angering civilians and risking sectarian bloodshed in the Sunni-dominated area. The group has also been accused of spreading violence and looting in other areas.

But a Sunni tribal leader, Naeem al-Gauoud, told The Associated Press that they would be welcomed after many tribal fighters died trying to defend Ramadi, with their bodies left in the streets or thrown in the Euphrates River.

“We welcome any group, including Shiite militias, to come and help us in liberating the city from the militants,” he added.

“What happened today is a big loss caused by lack of good planning by the military.”

Thousands of civilians fled the Isis advance in Ramadi (AP)

Shia militias had arrived at a military base near Ramadi by Sunday evening, said the head of the Anbar provincial council, Sabah Karhout.

John Kerry, the US Secretary of State, claimed he was confident that Isis could be driven out with the help of coalition air strikes.

"I am convinced that as the forces are redeployed and as the days flow in the weeks ahead (Isis’ control is) going to change," he added.

Civilian belongings can be seen in an abandoned truck during fighting in Ramadi (Reuters)

Bodies, some burned, littered the streets of Ramadi as officials reported that Isis carried out mass killings of Iraqi security forces and civilians.

A video posted online showed Humvees, trucks and other equipment speeding out of the city, with Iraqi soldiers gripping onto their sides.

A spokesperson for the Anbar government estimated that 500 people had been killed and 8,000 had fled the city, following another huge exodus in April, bringing the total of displaced people to 114,000.

Iraqis fleeing from their hometown of Ramadi walk on a street near the Bzebiz bridge, 65 kilometers (40 miles) west of Baghdad (AP)

The Prime Minister had ordered security forces not to abandon their posts across Anbar province, apparently fearing the extremists could capture the entire desert region that saw intense fighting after the 2003 invasion to topple Saddam.

But on Sunday Isis used bombings that killed at least 10 police officers to take the local headquarters and then detonated suicide bombs at the military’s Anbar Operation Command, the military headquarters for the province, killing five soldiers.

An Iraqi family, who fled the city of Ramadi after it was seized by Islamic State (IS) group militants, gathers inside a tent at a camp housing displaced families. (AFP)

The group seized the remaining Malaab district after government forces withdrew, taking control of the military headquarters and abandoned army vehicles and weapons including artillery and guns.

Isis is now believed to control around a third of Iraq, as well as vast swathes of neighbouring Syria.