The capture of Mosul and Tikrit by fighters of the Islamic State in Iraq and the Levant (Isis) have sent shockwaves across the Middle East, fuelling concerns about the growing strength of al-Qaida and other extremist groups that have already changed the contours of the war in Syria. These extraordinary events look set to push several countries, some of them bitter rivals, to make common cause against what has been dubbed the "jihadi spring".

Iran

Iran, a close ally of Iraq's Shia prime minister, Nouri al-Maliki, was quick to express support for the Baghdad government in the fight against what it described as "Takfiri militants" – a term associated with Sunni sectarianism. Tehran's position has raised the prospect of de facto cooperation with the US, which has called for "a strong and coordinated response" to the crisis and has also pledged to help Maliki fight al-Qaida. President Hassan Rouhani said his country could not tolerate violence and terror in the region. Iran is the main regional backer of the Syrian government.

Kurdish regional government (KRG)

The KRG, which runs the most stable and prosperous part of Iraq, has long been in dispute with Baghdad over oil revenues and territory. But the Isis threat looks likely to boost security cooperation with Maliki. That could see peshmerga fighters, the country's best-trained and motivated military force, take on al-Qaida. Kurdish units may well move deeper into disputed areas of Nineveh province and Kirkuk, reinforcing KRG ambitions to establish de facto authority over its energy-rich periphery, including areas near Mosul.

Turkey

Turkey's government has been meeting in crisis session in both Ankara and at Nato HQ in Brussels. It may decide to try to rescue 80 Turkish nationals being held hostage by Isis. The government has a mandate to conduct cross-border operations in Iraq, drafted to allow it to hit Kurdish PKK bases in the north of the country. Turkey has important interests in energy developments in Iraq. "Turkey is especially wary of the potential for attacks by Isis – attacks that would exploit the long border that runs from the Mediterranean to Iran," said the Stratfor consultancy. Turkey has lined up with the Syrian rebels.

A map of the key areas in Iraq. Photograph: Guardian

Syria

Isis has erased sections of the border between Iraq and Syria, where it controls Raqqa and other areas. Captured US-made Humvees supplied to the Iraqi army have been triumphantly displayed in Deir ez-Zor. Isis successes in Syria have expanded the group's sources of supplies and equipment. But mounting Arab and western anxiety about terrorism spreading to Europe may end up benefiting Assad, who has deftly presented himself as the best defence against extremism – even while he has, apparently, covertly encouraged it. But Syria's western-backed opposition may also push to present itself as the force that should be supported in order to fight Isis and other jihadis and build a free and democratic Syria. Assad has expressed solidarity with the Iraqi government.

Jordan

Jordan, which shares a long border with Iraq, is nervous about the growth of al-Qaida. It has the dubious honour of being the homeland of Abu Musab al-Zarqawi, the founder of al-Qaida in Iraq. The staunchly pro-western monarchy has devoted considerable efforts to forestalling terrorist attacks since 2005, when al-Qaida hotel bombings in Amman killed 60 people. Its intelligence service, which cooperates closely with its western counterparts, is renowned as the most professional in the Arab world. Jordanian analyst Oraib al-Rantawi called for increased coordination with both Baghdad and Damascus to contain the threat. Isis recently posted a video threatening to "slaughter the tyrant" – King Abdullah. Terrorists who appeared in the video were Jordanians who tore up their passports and vowed to launch suicide attacks inside the kingdom.

Saudi Arabia

Saudi Arabia and other Gulf states have been accused of funding extremism in Iraq and especially in Syria. Individual businessmen and clerics from Kuwait to Qatar are known to finance Isis and groups such as the Syrian Jabhat al-Nusra, though governments have cut back support and pledged to coordinate more closely with the US in backing only vetted and non-jihadi Islamist fighting units. The recent dismissal of the veteran Saudi intelligence chief Prince Bandar bin Sultan and his replacement by Prince Mohamed bin Nayef, who led the fight against AQ in the kingdom, reflects a sharper counter-terrorist focus created by fears of Afghan-style "blowback" from returning fighters. Earlier this month the Saudi authorities announced that citizens caught travelling to Iraq will face hefty fines and a three-year travel ban.