Iran is ready to help Iraq fight an armed uprising using the same methods it deployed against opposition forces in Syria, an Iranian general said, suggesting Tehran was offering to take a larger role in battling Sunni armed groups threatening Baghdad.

Iranian leaders to date have said they would help defend Shia Muslim shrines in neighbouring Iraq if necessary, but have also said Iraqis were capable of doing that job themselves.

Iran's Supreme Leader Ayatollah Ali Khamanei last week said that he rejected intervention in Iraq by Washington or any other outside power against Sunni fighters from the Islamic State of Iraq and the Levant (ISIL) group.

ISIL has seized a broad swathe of territory in northern and western Iraq in recent weeks in their quest to topple the government of Prime Minister Nouri al-Maliki, a Shia-backed by Iran, and to set up an Islamic caliphate.

Brigadier General Massoud Jazayeri, deputy joint chief of staff of the armed forces and a senior Islamic Revolutionary Guards Corps (IRGC) officer, told Iran's al Alam television that Iran's response to the militias would be "certain and serious".

The Iranian general said that his country would deal with Iraq on defence, security, border control and fortifications. To help Iraq, he said, Iran would monitor the situation in the region, as it had done "in Syria and other troubled areas in the region".

'Successful experiments'

Jazayeri's remarks late on Saturday did not provide details on the assistance Iran could give Baghdad, beyond saying Iran could help with what he called popular defence and intelligence.

"Iran has told Iraqi officials it is ready to provide them with our successful experiments in popular all-around defence, the same winning strategy used in Syria to put the terrorists on the defensive ... This same strategy is now taking shape in Iraq - mobilising masses of all ethnic groups," he told the television station.

"A response is certain and serious," he said.

Shia Iran has spent billions of dollars propping up its ally, Syrian President Bashar al-Assad, in what has turned into a sectarian proxy war with Sunni Arab states.

The help has included hundreds of military specialists, including senior commanders from the elite Quds Force, the external and secretive arm of the IRGC, according to Iranian sources familiar with deployments of military personnel.

Assad has also received battlefield support from fighters of the Lebanese Hezbollah movement, which Tehran also backs.