Iran vowed revenge on Britain and the US yesterday after blaming them for a devastating suicide attack against the elite Revolutionary Guards that killed 42 people, including six senior commanders.

The bombing, at a Revolutionary Guards gathering in the turbulent southeast of the country, was the worst attack on the powerful unit in recent years. Responsibility was swiftly claimed by Jundallah, a militant Sunni group that has regularly attacked the Guards in its battle against the Government and the Shia majority. It is thought to operate across the lawless border with Pakistan.

Last night Islamabad’s Ambassador to Tehran was summoned to the Iranian Foreign Ministry, which protested against “the use of Pakistani territory by the terrorists” against Iran. But the harshest words were reserved for the US and Britain, which Tehran accused of backing Jundallah in an attempt to overthrow the Islamic regime. The Guards blamed the bombing on “terrorists” backed by “the Great Satan America and its ally Britain”.

An official military statement added: “Not in the distant future we will take revenge. There is no doubt that this savage and inhuman act falls within the Satanic strategy of the foreigners and enemies of the regime, who are trying to break the unity among the Shias and Sunnis.”

Iranian state television quoted “informed sources” who said that the British Government was directly involved in the attack by “organising, supplying equipment and employing professional terrorists”.

The accusations increased tensions with the West a day before six-party talks in Vienna today over Iran’s nuclear programme. In Geneva this month Iran agreed in principle to a deal in which most of its low-enriched uranium stockpiles would be transferred overseas for further processing — a compromise that the West hopes will help to thwart the diversion of nuclear fuel to a suspected weapons programme. A failure to sign off on the details of that deal today would question Iran’s sincerity to address international concerns.

President Ahmadinejad of Iran warned of swift retribution against those who carried out the attack. “I am ordering the relevant officials to identify quickly the elements of this terrorist crime and hand them over to the judiciary,” he said.

Ali Larijani, the parliament’s hardline Speaker, accused the US of ordering the bombing and reneging on its new policy of engagement with Tehran. “Mr Obama has said he will extend his hand towards Iran, but with this terrorist action he has burnt his hand,” he said.

Britain and the US firmly denounced the attack and the claims of their involvement. “We reject in the strongest terms possible the assertions that this has anything to do with the UK,” a spokesman for the Foreign and Commonwealth Office said. The State Department in Washington added: “Reports of alleged US involvement are completely false.”

The attack was a serious blow for the Guards at a national as well as a local level. The dead reportedly included the deputy commander of the Guards’ ground force, General Noor Ali Shoushtari, as well as a chief provincial Guard commander for Sistan-Baluchistan province, Rajab Ali Mohammadzadeh. General Shoushtari was also a senior official of the powerful al-Quds force, an elite intelligence unit within the Guards.

The commanders were travelling to a meeting in the city of Pishin, near the border with Baluchistan province in Pakistan when an attacker blew himself up next to their convoy.

Jundallah — meaning “Soldiers of God” — has waged a low-level insurgency, carrying out bombings and kidnappings, including an attack in February 2007 that killed 11 members of the Guard near Zehedan. Iran has resisted taking major military action against the group for fear of stirring up a ShiaSunni battle that could draw in Sunni militants, including al-Qaeda, particularly from neighbouring Pakistan.

Iran has accused Britain and the US of funding and backing Jundallah. Reports have surfaced in recent years from anonymous CIA sources who say that money is channelled to the group to sow discontent in Iran. Britain and the US have officially denied involvement in such activity.

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