A surge in accusations

US military spokesmen, officials and analysts are gradually adding flesh to the bones of earlier allegations of official Iranian collaboration with Shia and Sunni insurgents in Iraq, including elements linked to al-Qaida.

The development comes amid reports that the White House is leaning towards military action against Iran over its suspect nuclear activities and supposed meddling in Iraq - and growing domestic pressure on George Bush to show the Baghdad military "surge" is working.

A senior US official in Baghdad told the Guardian in May that Iran was fighting a proxy war in Iraq. He accused Tehran of "committing daily acts of war against US and British forces". Its actions included weapons and other assistance to militias and ad hoc cooperation with individual extremists tied to al-Qaida, he said.

The allegations were rejected out of hand by Iran. Anti-war groups dismissed them as unsubstantiated US propaganda, reminiscent of false claims made prior to the 2003 invasion of Iraq.

Similar statements by British officials, to the effect that Iran has supplied roadside bombs known as improvised explosive devices to insurgents in Basra, have previously been flatly denied by Iranian diplomats.

In apparent response to this continuing scepticism, Brigadier General Kevin Bergner put the concerns of the US-led coalition on the record at an official briefing in Baghdad on July 2.

For the first time Gen Bergner formally accused Iran's senior leadership, acting through its al-Quds force and Lebanese Hizbullah, of instigating, or at the very least countenancing, insurgent attacks. He cited one specific incident in Kerbala in January, which resulted in the deaths of four Americans, and identified 21 "high-level operatives" who worked under clandestine Iranian direction.

"We are operating against secret cells or special groups funded, trained and armed by external sources, specifically by Iranian Revolutionary Guard Corps Quds Force operatives," Gen Bergner said.

He stressed the amorphous nature of the groups that he said included "rogue elements" from various backgrounds, Iraqi and external, united by a wish to fight.

Gen Bergner indicated that interrogations of captured insurgents were partly the basis for the US intelligence assessments. He detailed alleged al-Quds involvement in training, at camps inside Iran, weapons supply, and funding of the special groups to the tune of $3m a month.

Unidentified western officials went even further a few days later. They told the Financial Times they had evidence that Iran was allowing its territory to be used as a money and communications hub by al-Qaida operatives and by Iraqi Sunni insurgents fleeing coalition action.

"The most conservative, cautious intelligence assessment is that they [the Iranian authorities] are turning a blind eye. But there are a lot of doubts about that," a senior US official told the FT. "They are benefiting from the mayhem that al-Qaida is carrying out. They don't have to deal with al-Qaida to benefit."

A former Iranian official said that while there was a "successful intelligence relationship" with al-Qaida, Tehran did not supply the group with weapons and kept it at a distance.

Speaking in London this week, Frederick Kagan, a West Point military historian and noted US neoconservative who helped inspire Mr Bush's surge plan, said there was no "smoking gun" proving direct, continuous, high-level collaboration between al-Qaida and other Sunni extremists and Iran's top leaders.

But Dr Kagan said a growing body of evidence suggested that previous patterns of Iranian military and other assistance to Shia militias were now being repeated with respect to Sunni jihadis of all descriptions, including individual cells of al-Qaida - although not the movement as a whole.

The evidence was often circumstantial, he said, but included Iranian-manufactured and Iranian-purchased arms caches found in al-Qaida and Sunni-dominated areas, such as a factory in Samarra and another in Muqdadiya, near the Iran border. Discovery of the bases had led to a retaliatory al-Qaida attack, he said. Training camps in Iran had also been located.

"The Iranians and al-Qaida both want the Iraqi state to fail. If Iran wanted a stable Iraq, they would be supporting the Shia government of the [prime minister Nuri] al-Maliki," Dr Kagan said. Tehran's prime motive was to ensure Iraq never again threatened Iran, as it had under Saddam. But it also wanted to "keep us bleeding" in Iraq.

"Iran is supplying everybody who is engaged in violence, every faction, every accelerant of violence, including [the Shia militia] Jaish al-Mahdi and al-Qaida. This is all too well organised to be happening without regime knowledge."

Dr Kagan said he did not pretend to understand the Iranian leadership's longer-term strategy in Iraq or vis-a-vis future relations with the US. But he was pessimistic that increased diplomatic contacts would bring a change of policy - on either side.

There was no sign, he said, that Iranian interference in Iraq would end any time soon. Nor was Mr Bush going to abandon the surge, which would probably continue until at least summer next year, whatever Congress might say in September.

Under such a scenario, and with the US ever more convinced it is under sustained assault, the potential for direct confrontation with Iran can only grow.

Simon Tisdall