The claim threatens a new political storm over how and why FBI officials and MI5 operatives in the early 1990s conspired to supply deadly bombmaking equipment to the Provisional IRA in the early 1990s, mechanisms the paramilitary organisation later shared with Palestinian fighters.

The same technology is now being used by insurgents in Iraq.

Britain's Secretary of State for Defence John Reid was forced into a humiliating retraction six months ago, when the UK's Independent on Sunday newspaper first reported the claims. His officials had repeatedly insisted that bombs which killed eight British soldiers in separate attacks in Basra had been supplied to foreign fighters by Iran's Revolutionary Guard.

However, the newspaper reported that the technology had in fact first been used in Newry, Co Down, in 1992 to murder a policewoman and maim her male colleague. Kevin Fulton, a former soldier who infiltrated the IRA on behalf of the security services, claimed that he had flown to New York, met FBI and MI5 agents and was given money to buy an infrared device to be used to set off IRA bombs. The security services believed that by supplying the equipment they could then introduce counter measures.

"They knew the IRA was looking at the technology. By supplying the equipment, they thought they could stay one step ahead of the IRA, " Fulton said yesterday.

In an article to be published next week, the respected American magazine Atlantic Monthlywill now claim that FBI sources have confirmed Fulton's trip to the US. Atlantic Monthly reporter Matthew Teague said he was aware that a number of senior US politicians were awaiting the article's publication before raising the issue in Congress.

Fulton currently lives in hiding in England and is taking a legal action against the UK's Ministry of Defence, insisting he should receive a soldier's pension. A former member of the Royal Irish Rangers, the Co Down man infiltrated the IRA after being recruited directly from the regiment by the shadowy army outfit the Force Research Unit, which ran agents inside loyalist and republican organisations.

Teague says Fulton answered "No comment" to claims that he had been responsible for 11 murders while working as an agent and that he had been given carte blanche to kill by his handlers.

Fulton yesterday refused to comment on those claims again but, when asked about his New York arms-buying trip, he said: "I have been in touch with representatives of some senior American politicians in the past few days and I've told them that I am willing to travel back [to the US] and appear before Congress if necessary."

The Police Ombudsman in Northern Ireland has been investigating the FBI/MI5 link to the murder of Constable Colleen McMurray, 34, who was killed when an IRA Mark 12 mortar hit the passenger side of her patrol car as it travelled along Merchants Quay, Newry on 26 March 1992.