Ayatollah Khamenei has authorised his top commander to co-ordinate military operations with the US, Iraqi and Kurdish forces, sources in Tehran say.

Iran has traditionally opposed US involvement in Iraq, an Iranian ally.

Shia Iran sees the extremist Sunni IS group, which views Shias as heretics, as a serious threat.

Last month US air strikes helped Iranian-backed Shia militia and Kurdish forces break a two-month siege by Islamic State of the Shia town of Amerli.

IS has taken over swathes of northern and western Iraq and eastern Syria in recent months.

Sources say Ayatollah Khamenei has sanctioned Gen Qasem Soleimani, the commander of the Quds Force - an elite overseas unit of the Revolutionary Guards - to work with forces fighting IS, including the US.

Gen Soleimani has been active in the past few months in strengthening the defences of Baghdad with the help of Iraqi Shia militias.

'No boots on the ground'

Meanwhile, Nato leaders meeting at a summit in Wales say they want to form a military coalition to take on IS.

"We need to attack them in ways that prevent them from taking over territory, to bolster the Iraqi security forces and others in the region who are prepared to take them on, without committing troops of our own," Reuters news agency quotes US Secretary of State John Kerry as saying.

"Obviously I think that's a red line for everybody here: No boots on the ground," he said.

The brutality of IS - including mass killings and abductions of members of religious and ethnic minorities, as well as the beheadings of soldiers and journalists - has sparked outrage across the world.

Last month Iraqi and Kurdish forces pushed IS back from parts of northern Iraq, but the group still controls what it has declared as a caliphate stretching across Syria and Iraq.

(source: bbc.co.uk)