Iran has stepped up surveillance along its long border with Iraq in precaution against a spread of violence from militants who have siezed a swathe of its neighhour, a senior official said.

Sunni Islamists from the Islamic State in Iraq and the Levant (ISIL) have mounted a lightening advance toward the Iraqi capital, seizing territory in their quest for a border-less caliphate, spanning the region.

"Due to the unique situation in Iraq and its proximity to our western regions, we have taken duly precautions to shore up control, watch and fortifications along the border," Interior Minister Abdolreza Rahmani-Fazli told reporters.

"But presently we have no worries," the minister was quoted as saying by the official news agency IRNA.

The ISIL movement consists of an amalgam of Sunni tribesmen, militants and loyalists of former Iraqi President Saddam Hussein, sharing little but their hatred of the Shi'ite-led government in Baghdad.

Ruled by Shi'ite Muslim clergy, Iran has been rattled by the advance of ISIL in Iraq. Tehran has warned it might act to protect sacred Shi'ite shrines in the neighbouring country.-Reuters