LONDON [MENL] -- A series of blasts that rocked the British capital was believed to have been carried out by a new Al Qaida network based in Western Europe and trained in such places as Afghanistan, Bosnia and Iraq.

At least 50 people were killed in three explosions in London's subway system during rush hour on Thursday in a strike that resembled the train bombings in Madrid in 2004. A fourth explosion destroyed a double-decker bus filled with people.

An organization called "The Secret Organization of Al Qaida in Europe" claimed responsibility for the blasts, in which 700 people were injured. Western intelligence sources said the group appeared to represent a new generation of Al Qaida operatives aided by at least two major organizations based in Algeria and Iraq. They said the attacks were meant to disrupt the G8 summit in Scotland.

"Over time, the cornerstone of Al Qaida's religious and political rhetoric has remained consistent: Muslims should view themselves as a single nation and unite to resist anti-Islamic aggression on the basis of obligatory defensive jihad," a Congressional Research Service report, entitled "Al Qaida: Statements and Evolving Ideology," authored by Christopher Blanchard, said.