The New York Times says in its Sunday edition that U.S. government investigators have examined fragments from hundreds of improvised explosive devices used in attacks on the three continents and have found design similarities in many of them.

The newspaper quotes one forensic expert as saying many devices were made by the same bombmaker or by different people using the same bombmaking instructions.

The Times report says intelligence analysts suggest that the al Qaida terrorist network may be teaching bombmaking skills to militants who now are spread around the world.

Some counterterrorism experts believe efforts should be focused on capturing the relatively small number of master bombmakers responsible for building bombs used in most large-scale attacks.

According to the Times, the United States has established a new forensic intelligence unit to gather information related to the construction of improvised explosive devices.

The unit, known as the Terrorist Explosive Device Analytical Center, or TEDAC, says nearly all terrorist attacks against Americans in the last five years involved improvised bombs.

Tedac began operating in December, but The New York Times says Congress was made aware of its existence only last week.