London bombs were of "military origin"

European investigators believe that the bombs used in Thursday's attacks on London's transport network contained "military quality" high-grade explosives.

The investigators said they still don’t know whether the explosives contained plastic materials.

But they said the material used in the bombs was similar to the kind made for military use or for highly technical commercial purposes, such as dynamite used for precision explosions to demolish buildings or in mining.

''The explosives appear to be of military origin, which is very worrying,'' said Christophe Chaboud, chief of the French Anti-Terrorism Coordination Unit and one of five senior officials sent by Paris to London immediately after the attacks.

''We're more used to cells making home-made explosives with chemicals. How did they get them?'' he said in an interview with Le Monde newspaper.

''Either by trafficking, for example, in the Balkans, or they had someone on the inside who enabled them to get them out of a military establishment.''

Some investigators initially said that the bombs were relatively crude due to their small size, estimated at 4.5 kilograms, or 10 pounds.

By comparison, the ten bombs that hit four commuter trains in Madrid last year weighed about 10 kg each. The explosive, known as Goma 2 Eco and used in quarrying, had been stolen from a mine in northern Spain.

Another top European-based counterterrorism official said the new information on the explosives material means that the bombs were "technically advanced."

"There seems to be a mastery of the method of doing explosions. This was not rudimentary. It required great organization and was well put together," he said.

The quality of the bombs made many investigators think that the explosives were assembled by at least one technically savvy bomb maker, who might have traveled to Britain to make the devices for use by a local "sleeper cell," officials said.

"People assume you can look up a bomb-making design on the Internet and put one together without any training," said one top counterterrorism official based in Europe. "But it's not that simple or easy."

Investigators say that determining the physical origin of the explosives will lead to the origin of the bombs.

British intelligence officials asked their European counterparts to scour military stockpiles and commercial sites for missing explosives, three top European-based intelligence officials said.

Top officials fear that the attackers might have a stockpile of more explosive material and could strike again, in Britain or in another European country.

"I really pity my British colleagues," a top European intelligence official said. "It's a very difficult situation. Every hour that passes diminishes the probability to catch those people and increases the chances that this cell might try to strike again."