DHAKA: Iraq’s most senior Shia cleric has issued a call to arms as Sunni-led insurgents seize more towns.

The call by a representative of Grand Ayatollah Ali al-Sistani came during Friday prayers, as the militants widened their grip in the north and east, and threatened to march south.

The UN says hundreds have been killed with militants carrying out summary executions of civilians in Mosul, reports the BBC.

Both the US and Iran have promised to help the fight against the insurgency.

Led by the Islamic State in Iraq and the Levant (ISIS), the Sunni insurgents have threatened to push to the capital, Baghdad, and regions further south dominated by Iraq's Shia Muslim majority, whom they regard as “infidels”.

In his sermon at Friday prayers in Karbala, Sheik Abdulmehdi al-Karbalai said, “Citizens who are able to bear arms and fight terrorists, defending their country and their people and their holy places, should volunteer and join the security forces to achieve this holy purpose.”

 There are reports that thousands have already joined Shia militias which could play a crucial role in the defence of Baghdad, says the BBC’s Richard Galpin there.

According to the Wall Street Journal - which cited unnamed sources - Iran has already deployed two battalions of the elite al-Quds forces of its Revolutionary Guard to help the Iraqi government.

US President Barack Obama said he did not “rule out anything because we do have a stake in making sure these jihadists are not getting a permanent foothold in Iraq, or Syria for that matter”.

BDST: 2012 HRS, JUNE 13, 2104