Tony Blair today warned Iran not to "interfere" in Iraq, after publicly accusing the republic or its allies of supplying sophisticated roadside bombs used to kill coalition troops in Iraq.

The Prime Minister's intervention, in a news conference after a meeting with the Iraqi President Jalal Talabani in Downing Street, will intensify the diplomatic rift between the two nations.

He said that armour-piercing bombs, triggered by infrared "trip-wires", which have become a recent feature of insurgent attacks on troops in Basra, could be traced back to Hezbollah, the Tehran-backed militia based in Lebanon.

"There are certain pieces of information that lead us back to Iran, however we cannot be certain of this at the present time," he said.

"What is clear is that there have been new explosive devices used, not just against British troops but elsewhere in Iraq. The particular nature of those devices leads us either to Iranian elements or to Hezbollah, because they are similar to the devices used by Hezbollah."

The accusation first surfaced yesterday when a senior British official, briefing journalists on condition of anonymity, said that Iran's Revolutionary Guard was supplying technology and training that had led to the deaths of six British soldiers and two British civilians over the summer.

The most recent death was that of Major Matthew Bacon, of the Intelligence Corps, who died when a roadside bomb was detonated in Basra on September 11, destroying his armoured Land Rover.

Mr Blair confirmed these allegations and went further, warning Iran not to interfere in the ongoing battle against the insurgency in post-war Iraq.

He said that Shia Iran may have begun to intervene in the mainly Sunni-led insurgency in south Iraq to punish Britain's tough stance over its nuclear programme.

Talks have collapsed and Iran today said it was making steady progress on its uranium enrichment programme, which the West fears is a smokescreen for the development of nuclear weapons.

"Will we not be subject to any intimidation in raising the necessary and right issues to do with the nuclear weapons obligations of Iran under the Atomic Energy Agency treaty," he said.

"I want to make it very, very clear - and this been made clear to the Iranian government and I make it clear again - the British forces are in Iraq under a United Nations mandate. There is no justification for Iran or any other country to interfere with Iraq."

Tehran has fiercely denied the claims, which Foreign Ministry official Hamid Reza-Asefi denounced as "fantasy".

Appearing on state television last night, he said: "Britain's conspiracies have been revealed and its scandal in Iraq has made London make up this lie. The British are the cause of instability and crisis in Iraq. By drafting such scenarios they are trying to find a partner in their crimes."

It is the first time that the long-suspected link between the Iraqi insurgents and their neighbours has been declared officially. The United States has for some time been openly accusing Tehran of supporting and influencing the insurgents' attacks on coalition troops in Iraq.

President Talabani was visiting Britain today as violence in Iraq escalated in the run-up to a referendum on the post-Saddam constitution on October 15.

Confidence in the poll, already dismissed by the minority Sunni community, has been further damaged by a humiliating volte face on voting rules.

Mr Blair strived to reassure the President that the ballot would be successful in the British-controlled southern regions.

The interim Iraqi government has emphasised that a smooth and well-attended ballot, mirroring that of January's interim elections, is an essential step for the country's political and physical rehabilitation.

Some five million copies of the charter were being distributed across the country today for citizens to collect from their local shops when they pick up their food rations.

Military sources have warned of an inevitable upsurge in violence in the run-up to the poll.

Their fears appear to have been borne out in the past 24 hours with 13 people including a US soldier killed in Baghdad this morning, and 25 Shia Muslims left dead after a bomb attack on a mosque in the southern town of Hilla.

Sunni leaders have called for a boycott of the poll, because its federalist principles will fracture the country into three separate regions: a Kurdish north and Shia south, controlling Iraq's oil wealth, with a poor majority Sunni area in the central war-ravaged deserts.

The unease was heightened this week when the Shia-led National Assembly changed electoral rules which would have made a "no" vote virtually impossible.

They were switched back yesterday under heavy criticism from the United Nations and the US, although the reversal has underlined accusations that interim Prime Minister, Ibrahim Jaafari, is exceeding his authority.

Although he publicly denounced Mr Jaafari earlier this week, President Talabani, a Kurd, last night rejected calls from his party's official spokesman to sack the Prime Minister: "We don't think this is the time to change the government now," he told a news conference.

The October 15 vote on the draft constitution is seen as a key milestone in Iraq's political transition following Saddam's downfall in April 2003, and is due to be followed by fresh elections in December.

By Simon Freeman
www.timesonline.co.uk