The US military last night raised the stakes in Washington's war of words with Tehran by claiming the "highest levels" of the Iranian government were responsible for supplying roadside bombs that have killed and maimed almost 800 American troops in Iraq.

For years, US officials have claimed weapons used by Iraqi insurgents have originated from across the border in Iran but have stopped short of directly accusing President Mahmoud Ahmadinejad's government.

Yesterday, however, in a private media briefing in Baghdad three military specialists - a defence official, a defence analyst and an explosives expert - claimed there was a "growing body of evidence" that Iranian-made weapons were being used to murder coalition forces. It was suggested that between June 2004 and last week, so-called "explosively formed projectiles" (EFPs) made in Iran and smuggled into Iraq had been responsible for killing more than 170 American troops and wounding around 620 more. An EFP has the power to pierce the armour of a US Abrams tank.

One of the specialists said Tehran was using "multiple surrogates" - mainly rogue elements of the Shia Mahdi Army - to smuggle EFPs into Iraq. The Iranian government was also providing money and training to Shia insurgents, it was further claimed.

Mr Ahmadinejad, who yesterday marked the 28th anniversary of Iran's revolution by pledging to pursue the country's controversial nuclear programme, denies all the charges.

It was said most of the bomb components were entering Iraq at crossing points near Amarah, the Iranian border city of Meran, and through the British-controlled Basra area of southern Iraq.

While it was claimed orders for the smuggling of EFPs came from the top of the Iranian government, no details such as names were given. The analyst said Iraq's Shia-led government had been briefed on Iran's involvement and Iraqi officials had asked the Iranians to stop.

In the Iraqi capital, journalists were shown fragments of what the American defence official said were Iranian-made weapons, including one part of an EFP and tail fins from mortar bombs. He noted: "The weapons had characteristics unique to being manufactured in Iran." Reporters were told the dates of manufacture on the weapons found so far indicated they were made after the fall of Saddam Hussein, mainly in 2006.

The analyst said the "machining" on the components was traceable to Iran.