Di Suleiman Abdullah al-Alawi – Head of the Iraqi intelligence service – said the group’s aim remains to attack security forces and civilians in Baghdad.

“Even though our forces are not strong, we will continue our operations to harm security forces and civilians in Baghdad,” he said.

An Iraqi government source said the group has recruited around 2,000 fighters across the country who have trained with the assistance of neighbouring countries.

The source said the militants attacked a military prison at the main airport in Baghdad on Friday, and that the group had also seized parts of two main army bases, one of them at Fallujah, home of the army’s Ninth Division.

Troops loyal to the Shia government and troops backed by US-led coalition air strikes battled the militants in large swaths of western Iraq earlier this week.

On Friday, the US-led coalition said it conducted a strike in which it destroyed two vehicles used by the militant Islamic State of Iraq and the Levant in Sirte, home to the main city of the Islamist militants.

The coalition also said it destroyed an artillery system that was used by the militants to fire rocket-propelled grenades at positions the Iraqi government held.

The Syrian army earlier this week claimed to have killed 10 militants of the IS group in a joint operation along the border with Jordan, where it is battling Islamic State.

The Syrian government, which says IS has been pushed back, is also battling IS-linked groups in the area.