A RADICAL plan by Al-Qaeda to take over the Sunni heartland of Iraq and turn it into a militant Islamic state once American troops have withdrawn is causing alarm among US intelligence officials.

A power struggle has emerged between the self-styled Islamic State of Iraq, an organisation with ambitions to become a state which has been set up by Al-Qaeda, and more moderate Sunni groups. They are battling for the long-term control of central and western areas which they believe could break away from Kurdish and Shi’ite-dominated provinces once the coalition forces depart.

According to an analysis compiled by US intelligence agencies, the Islamic State has ambitions to create a terrorist enclave in the Iraqi provinces of Baghdad, Anbar, Diyala, Salah al-Din, Nineveh and parts of Babil.

“Al-Qaeda are on the way to establish their first stronghold in the Middle East,” warned an American official. “If they succeed, it will be a catastrophe and an imminent danger to Saudi Arabia and Jordan.”

The US conviction that the Islamic State could seize power is based on its use of classic Al-Qaeda tactics and its adoption last October of a draft constitution. This was entitled Notifying Mankind of the Birth of the Islamic State and was posted on a website based in Britain. The group named 10 ministers under its emir, Abu Amer Al-Baghdadi. They included a war minister, Abu Hamza Al-Muhajer who is also known as Abu Ayub al-Masri and is Al-Qaeda’s commander in Iraq.

Last week the Islamic State released a video that showed the execution of five Iraqi army soldiers and four police officers.

The Islamic State’s ruthlessness, combined with extreme religious fundamentalism, marks it out from other Sunni factions.

As well as the nine victims shown on the video, the group claimed to have captured an Iraqi army colonel and two of his bodyguards. They threatened to kill him within 24 hours unless demands to release Al-Qaeda sympathisers were met.

The Islamic State is spearheading the insurgency against US forces and troops loyal to Nouri al-Maliki, the prime minister. In recent months it has been responsible for chlorine gas bombs and numerous suicide attacks on civilian targets.

It is also behind the deadliest roadside bombs that have racked up American casualties this year, although US military sources are now confident that in recent weeks they have gained the upper hand with raids aimed at both the Islamic State’s leadership and its bomb-making factories. “The mood is positive but not foolishly so,” said a Pentagon source last week. “The marines are confident they’ve pushed the bad guys out. There is an element of propaganda about the all-powerful Al-Qaeda.”

The Islamic State’s brutal targeting of fellow Sunnis has made it unpopular among some who see Al-Qaeda as foreign influenced and too ready to attack Iraqis as well as US forces.

According to American diplomats, one of the topics of the visit to Saudi Arabia yesterday by Dick Cheney, the US vice-president, was Al-Qaeda’s power in Iraq.

Five US soldiers were killed and three were missing after their unit was attacked in a Sunni insurgent stronghold south of Baghdad yesterday. Additional reporting: Sarah Baxter, Washington

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