Iraq army volunteers
Volunteers, who have joined the Iraqi Army to fight against predominantly Sunni militants, carry weapons during a parade in the streets in BaghdadReuters

Senior SAS officials are on their way to Iraq after Britain and the US sent a "counter-terrorist" team to the oil-rich country, as Sunni jihadists continue their violent campaign to take control of Baghdad.

According to a report in the Sunday Times, senior British officers have been tasked with establishing potential targets as the US weighs up a possible bombing campaign against Sunni militant groups in the country.

Iraq has fallen into chaos after an extreme Sunni militant group, the Islamic State of Iraq and the Levant (Isis), took control of the country's second city of Mosul.

Located in the north of the country, Mosul fell after much of the regular Iraqi army dropped their weapons and fled in the face of Isis attacks.

Having seized Mosul, Isis and a coalition of radical Sunni militant groups took control of Tikrit and parts of Baiji, vowing to enter the Iraqi capital Baghdad next.

The rapid advance of the group, which espouses an ultra-conservative interpretation of Islam, has spooked regional players.

US President Barack Obama said he is considering "options," while the US's long-term adversary Iran has sent thousands of troops and the head of its elite Quds force to run the Iraqi military operation against the rebels.

Writing in the Independent on Saturday, Colonel Lieutenant Richard Williams urged the United States and the United Kingdom to intervene in Iraq.

Williams, who led SAS undercover operations during the Iraq war, said the group pose a threat to national security in those countries. He advised against sending conventional troops but backed a modest presence of specialist forces.

"This is not something we can just leave the Iraqis to solve," he wrote. "The reason we are sending people to Iraq is to support the government, contain the situation because if the situation escalates, it will because it's al-Qaida connected, threaten the UK directly, our interests abroad and our interests in the Middle East."