"Linkages have been made in devices that have been used in different continents," the New York Times quoted a forensic scientist involved in a newly set up intelligence unit as saying.

"We know that we have the same bomb maker, or different bomb makers are using the same instructions."

And while intelligence analysts have said they believe al-Qaida has been weakened by anti-terrorism campaigns, the bomb investigations suggest that it may still be disseminating bomb-making instructions to militants around the world, the New York Times reported.

The new forensic unit behind the effort to analyse bombs used in attacks is called the Terrorist Explosive Device Analytical Centre, or Tedac.

Terrorism specialists in Congress were briefed on the previously undisclosed intelligence operation's work this week, it said.

"Tedac is a multi-agency effort to analyse improvised explosive devices," the report quoted Dwight Adams, director of the FBI laboratory as saying.

"It gathers and shares intelligence related to the construction of these devices. Its purpose is to save lives."

Multi-agency unit

"Linkages have been made in devices that have been used in different continents. We know that we have the same bomb maker, or different bomb makers are using the same instructions"

US forensic scientist

According to the FBI, which took the lead in the centre's creation, almost 90% of attacks against Americans over the last five years have involved improvised explosive devices.

The unit, based at the FBI lab in Quantico, Virginia, began its work in December and lawmakers were told of its existence in recent days, the Times said.

It has drawn on input from a host of intelligence agencies including the Defence Intelligence Agency, the CIA, the National Security Agency and the Bureau of Alcohol, Tobacco and Firearms.

According to the Times, intelligence analysts believe followers of al-Qaida or sympathetic allies may be involved in some of the wave of bombings in Iraq, where none of the larger and most deadly suicide attacks have been solved.

Examination of bombs used in Iraq has thus far yielded little about who made them, it said.

Data bank

But the centre's experts have begun to compile a data bank of information about the bombs, and in some cases have been able to obtain evidence of who made the bomb through fingerprints or DNA material left behind, the Times said.

The study of the unexploded device built into the shoe of Richard Reid, a British citizen and al-Qaida sympathiser who was sentenced to life in prison for attempting to blow up a passenger jet over the Atlantic Ocean in December 2001, is a model of how the new centre will operate, the Times said.

Investigators found the design of the shoe bomb followed specific instructions in training manuals found by US forces at training camps in Afghanistan.

The investigators doubted Reid built the bomb, and found evidence such as a hair and fingerprints that proved others were involved.