LONDON -- The attempted bombings of London underground trains and a bus Thursday appeared less sophisticated than the deadly attacks that hit the British capital two weeks ago, but could suggest the existence of a new terror cell, terrorism experts said.
The London underground system was temporarily paralyzed after what police said were failed attempts to set off three bombs on trains and a fourth on a double-decker bus just after midday Thursday. Authorities reported one casualty. The explosive devices appeared to be smaller than the ones that exploded during rush hour on July 7, killing 52 people as well as the four suicide bombers, Metropolitan Police Commissioner Ian Blair said.
Jeremy Binnie, an analyst with the London-based Jane's Terrorism and Insurgency Center, said there were key differences between Thursday's explosions and the previous blasts.
The latest ones did not take place at rush hour, they targeted more outlying stations, and "if there were bombs, they seem to have been duds," Binnie said.
"It seems much more amateurish in many ways," he told The Associated Press.
That could suggest they were a copycat operation, but Binnie cautioned that it was too early to tell. He noted that investigations into the July 7 blasts showed signs there could be a second cell in existence.
Keith Burnet, an expert at the Royal Institute for International Affairs, a London-based think-tank, also said the blasts appeared to be part of a "copycat exercise, carried out by people not as sophisticated as the bombers who struck on July 7."
Burnet said there was little that Britain's security forces could do - short of searching every passenger on the capital's huge network of buses and trains - to thwart such attacks.
He said the quick response by police and medics may be partly credited to London's ongoing heightened state of alert from the quadruple bombings two weeks ago.
Paul Rogers, a terror expert at Bradford University in northern England, said investigators would have lots of forensic evidence to work on from the latest blasts.
"They will have the devices and much can be done to them in terms of fingerprinting, DNA, the origin of the detonators and where the bags were bought," Rogers said. "If this was a series of dummies deliberately timed to cause mass panic then it puts the people responsible at considerable risk of being found."
He also said the explosions could point to the existence of another terrorist cell in Britain.
"The one ominous thing is that this appears to be a group of a similar nature to the previous July 7 bombers," Rogers said. "It implies there might be another cell primed and ready to attack."