The Abu Hafs al-Masri Brigades (search), which said Friday it carried out the London bombings, has claimed responsibility for a wide range of attacks — and even for a massive U.S. power blackout.

Terror experts have cast doubt on the claims by the Al Qaeda-linked group, noting most are unsubstantiated and some clearly fakes. U.S. authorities, for instance, ruled out sabotage as the cause of the August 2003 blackout in the northeast.

The geographic spread of the group's claims also has raised skepticism. It has claimed attacks from Indonesia to Iraq to Istanbul, and some were later found to have been carried out by local Al Qaeda-linked groups.

Abu Hafs al-Masri, in fact, may be little more than a name used as an umbrella to give the appearance of a tightly formed Al Qaeda-linked global terror network.

Abu Hafs al-Masri was the nickname of Mohammed Atef (search), one of Al Qaeda leader Usama bin Laden's (search) most senior lieutenants, who was killed by a U.S. air raid in Afghanistan in November 2001.

It was one of two groups that said it carried out the deadly July 7 bombings in London. Friday's new Internet statement claimed responsibility for blasts Thursday that caused no casualties, and threatened more attacks in Britain, the Netherlands, Denmark and Italy.

In the past, threats issued in the brigades' name have warned of waves of attacks that in most cases did not occur, including vows to carry out bombings in Japan, Italy, Australia and Yemen.

The most deadly attack it has claimed was the March 2004 bombings against commuter trains in Madrid that killed 191 people. Investigators have said that attack was linked to Al Qaeda and carried out by Islamic extremists, but they don't know specifically what branch was responsible.