Iran has no interest in fomenting full-scale civil war in Iraq, but could stir trouble for the United States and Britain there if it felt threatened by international action to curb its nuclear ambitions.

Washington and London have long accused Tehran of playing a destabilising role in Iraq by backing Shi’ite militants and sending infiltrators and sophisticated bombs across the border.

Tehran derides the charges, but has also hinted in the past that it has the potential to inflict pain on its Western foes locally if they tighten the screws over the nuclear issue.

“If these countries use all their means ... to put pressure on Iran, Iran will use its capacity in the region,” Ali Larijani, secretary of Iran’s Supreme National Security Council, has said.

For now Iran appears to be holding back, wary of regional rivalries and the unrest that could arise among its own minorities if Iraq slid into outright civil war and fell apart.

“Iran has problems with its own Kurds, Arabs and Baluchis,” said Dubai-based analyst Mustafa Alani. “It has no strategic interest in Iraq’s disintegration. Other states will interfere.”

Rather than stoking sectarian tension, Iran’s Supreme Leader Ayatollah Ali Khamenei and President Mahmoud Ahmadinejad urged Shi’ites not to take revenge on Sunnis after last week’s bombing of a major Shi’ite shrine in Iraq, blaming the attack on the United States and Israel, rather than Sunni militants.

With its Iraqi Shi’ite allies already in the driving seat in Baghdad, Iran has much to lose if central authority collapses.

It has links to all the main parties in the United Iraqi Alliance, the Shi’ite bloc that dominated December 15 elections.

These are the Supreme Council for Islamic Revolution in Iraq, created by Iran as an exile opposition to Saddam during the 1980-88 war, Prime Minister Ibrahim Jaafari’s Islamist Dawa party, also based in Tehran before the 2003 invasion, and the movement of radical Shi’ite cleric Moqtada al-Sadr. While not slavishly obedient to Iran, these groups and the militias attached to them are at least sympathetic to Tehran, which also has long-standing links with the Kurdish parties.

“Whenever the Iranians come under pressure on the nuclear issue, like sanctions or military action, their answer will be in Iraq,” Alani said. “This is a major card for them.”

Toby Dodge, a London-based scholar, said Iran’s long-term interest was to have Iraq as a “stable vassal state” that would not grow into a rival for influence over the world’s Shi’ites.

“A territorially united Iraq would give them the lion’s share of influence, rather than just having (sway over) a Shi’ite breakaway state in the south,” he said. Iran would rather see the Sunni Arab-led insurgency contained — an aim it shares with Washington — and preserve a friendly Shi’ite-dominated national government, said Iran expert Anoushiravan Ehteshami, at Britain’s Durham University. Iran’s foreign minister bluntly told Britain on February 17 to remove its troops from Basra, saying they were destabilising the city. London accused Tehran of trying to divert attention from world concern over its nuclear programme.

Iran is happy to see the United States and Britain embroiled in Iraq, but does not want total chaos next door or a wider conflict that could draw in neighbouring countries.

A prolonged Iraqi civil war, with Baghdad at its vortex, might prompt Kurds to secede in the north and Shi’ites to take over the south, splitting Iraq’s oil resources between them and leaving little but desert for Sunni Arabs in the centre.

Iraq’s national unity, which survived a brutal eight-year war with Iran in the 1980s, has been tested as never before since the US-led invasion toppled Saddam Hussein in 2003.

“Iraq is teetering on the threshold of wholesale disaster,” said a report by the International Crisis Group this week, citing a Sunni-Shi’ite schism as the most urgent threat.

Iran may be as worried about this as Iraq’s Sunni neighbours in Jordan, Syria, Turkey, Saudi Arabia and the Gulf — many of whom are also deeply concerned about rising Shi’ite influence — but Tehran is better placed than most to advance its interests. Iran’s potential to make trouble in Iraq alarms Washington’s Arab allies, but Dodge said there was scant evidence that it was deterring the US-led drive to rein in Tehran’s atomic plans.

Alani said Iran was already the prime indirect beneficiary of US policies in the region since the September 11 attacks.