Thousands of Iraqis have responded to a call by the country’s most influential Shi’ite cleric to take up arms against a Sunni Muslim insurgency.

Around 800 Shi’ite men left the southern city of Basra on Sunday, heading to Baghdad for training to join the Iraqi army.

Local religious leaders encouraged them as they left.

The volunteers are facing danger even before they start fighting, with reports of a deadly mortar strike at a recruitment centre in central Iraq.

One of those gathered near a fleet of coaches waiting to leave Basra, Ibrahim Mohammed, said: “We have answered a call by Shi’ite clerics to go to Samarra which has been liberated and we will go to Mosul to liberate it from ISIL members, who are traitors and have no religion. They are neither Sunnis nor Shi’ites.”

Insurgents from ISIL – the Islamic State of Iraq and the Levant – have captured swathes of territory including the country’s second biggest city Mosul.

But after days of lightning advances, government forces have regained some territory in counterattacks. The defence ministry released footage saying it showed air strikes on Sunni militant targets in the north.

In Kirkuk, Kurdish forces are now in control. They, too, have been fighting ISIL.

Meanwhile the US is reviewing military options, short of sending troops, to combat the insurgency while Iran has offered its help to Baghdad, if a formal request is made.