Hand-carried travel equipment, including cameras and portable sound equipments, that could be taken without suspicion through US airport checkpoints, was found at terrorist hideouts, federal authorities told the magazine.

The discovery of the equipment hinted at how operatives of the Islamist militant network might go about launching an airline attack, retrieving the items after passing through airport security and using them to commandeer planes.

A bulletin from the US Homeland Security Department sent to airlines and leaked to the media said US intelligence had no reason to believe such equipment had yet been deployed.

However, sources told Newsweek that terrorists' efforts to manufacture such weapons-smuggling devices was worrying enough to warrant the hijack alert.

A key source for the information al-Qaeda's alleged leader in Saudi Arabia Ali al-Ghamdi -- also known as Abu Bakr -- a suspected brain behind the May bombings in Riyadh who turned himself in to Saudi authorities in June, Newsweek said.

Authorities were treating the information he gave with some reservations, the newsweekly added, although al-Ghamdi's information had been corroborated by other sources, including through electronic intercepts.

The United States Tuesday issued a fresh global terrorism warning to US citizens abroad -- updating its April 21 alert -- adding hijacking to a list of potential attacks US citizens may face following threats of al-Qaeda strikes similar to those of September 11, 2001, that killed more than 3,000 people.

The alert said hijackings could occur at worldwide locations including in the eastern United States, Britain, Italy or Australia. US officials told Newsweek al-Qaeda liked to "return to the scenes of the crimes."

One such location was the US Capitol building in Washington where Congress meets, believed to have been the intended target of the fourth plane in the September 11 attacks, which crashed instead into a field in Pennsylvania.

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