Iran may consider cooperating with its arch-foe the United States to fight Sunni extremist militants in Iraq, but has not yet received a request to intervene militarily across the border.
In the clearest indication so far that Iran may be pulled into the conflict, President Hassan Rouhani on Saturday admitted that turmoil caused by the Islamic State of Iraq and the Levant's (ISIL) advance towards Baghdad could have calamitous dimensions for the whole region.
Acknowledging his country's "close and intimate" relations with Iraq, Rouhani left the door open to some form of intervention when asked if mutual interest could possibly bring Iran and the US together.
"If we see that the United States takes action against terrorist groups in Iraq, then one can think about it," he said.
"We have said that all countries must unite in combating terrorism. But right now regarding Iraq... we have not seen the Americans taking a decision."
The State Department on Friday played down the prospect of cooperation, saying that though the US and Iran have "a shared interest" in what happens in Iraq there have been no talks.
It would be an unlikely alliance -- the two countries have had no diplomatic relations since the 444-days-long hostage crisis at the American Embassy in Tehran that followed the 1979 Islamic revolution.
Rouhani and US President Barack Obama, who have taken steps towards a thaw in relations in the past year, have separately pledged support for Iraqi Prime Minister Nuri al-Maliki's government.
Maliki's security forces are reportedly preparing a counter attack after losing the cities of Mosul and Tikrit, where some units ditched their uniforms and left their positions. But ISIL has not been contained.
However, dismissing reports that Iran had already sent troops across the border, Rouhani said no specific request for help has been made by Maliki, stressing that such a decision is for Iraq alone to make.
- US plans unknown -
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"I don't know of any American plans," he added, noting that Iranian help could include "consultation", a possible hint of military advisers being provided.
On Friday, Obama said a range of options short of sending troops was being considered, but he also suggested Iraq take its own steps to heal a sectarian divide many observers have blamed on Maliki.
But signalling that Iran is not at one with the US over the regional situation, Rouhani hit out at Western and Arab governments for backing rebels fighting to overthrow Syrian President Bashar al-Assad, an Iran ally, arguing that the jihadist surge in Iraq was a spillover from that conflict.
ISIL, employing brutal tactics and showing no mercy for civilians and rival rebels, has taken a swathe of mostly Sunni Arab territory in northern Iraq since launching an offensive on Monday.
Its advances and boasts of animosity toward Shiism -- a branch of Islam overwhelmingly practised in Iran -- have raised alarm in Tehran, though Rouhani said "the Iraqis can themselves repel terrorism".
He also praised a call to arms by Iraq's top Shiite cleric, Grand Ayatollah Ali al-Sistani.
Iran's border chief Hossein Zolfaghari, meanwhile, said security at the western frontier -- 1,458 kilometres (900 miles) of which is shared with Iraq -- has been bolstered.
Iranian media also quoted an intelligence official as saying 30 "Al-Qaeda-linked elements" had been arrested across Iran in the past month, but without stating if they were linked to ISIL.
Iran and Iraq, both predominantly Shiite, have strengthened their relations since the US-backed ouster of Sunni dictator Saddam Hussein in Baghdad in 2003.
Maliki spent years in Iran during the Saddam era, before returning after the invasion, eventually securing the premiership in 2006.
But with the country's democracy already seen as weak, and Maliki accused of marginalising Sunnis from the political process, the nation may yet break apart.
"The concern of everyone is that Iraq could split into separate Shiite, Sunni and Kurdish territories," said a Western diplomat in Tehran, noting the bond engendered by Shiite religious shrines in Iraq which hundreds of thousands of Iranians visit each year.
A senior Rouhani aide, Hamid Aboutalebi, has said the Middle East faces upheaval if ISIL is not stopped.
This week's battles could potentially trigger "the beginning of Iraq's disintegration into three countries of Kurds, Sunnis and Shiites," he said.