London police are investigating four small explosions on London's subway and bus system that wounded one person. The blasts come exactly two weeks after suicide terrorist bombs killed 56 people on the city's transport network.
The attacks Thursday were not on the same scale as the July 7 bombings that police have blamed on four British Muslim suicide bombers.
Still, the latest explosions have jangled the nerves of Londoners who worry the capital may experience more attacks from Islamic radicals angered at Britain's involvement in Iraq and Afghanistan.
London Police Commissioner Ian Blair says it is too early to connect Thursday's blasts with the July 7 attacks. He says police are hopeful that some unexploded devices will offer up important evidence.
"We do believe that this may represent a significant breakthrough in the sense that there is obviously forensic material at these scenes which may be very helpful to us, so I feel very positive about some of these developments," he said.
London Mayor Ken Livingstone is urging the capital's residents to show the same resolve they did during the Irish Republican Army bombing campaign of decades past.
"It is not surprising that we have had another attempt to take life in London so rapidly after the first," he said. "Those people whose memories stretch back to the terrorist campaigns in the 70s and 80s and early 90s will remember there were very often horrifying bombings in London, often only weeks apart. And we got through that and we will get through this."
One leading British security expert, Crispin Black, says police appear to have two theories about Thursday's attacks.
"Whatever was planned today, we've either experienced a nuisance bombing that doesn't really seem to have worked particularly well, and London is getting back to normal, or luck has been with us and we have escaped something worse," he said.
Witnesses say they heard small explosions on the subway trains that were hit, and they smelled what seemed to be burning insulation or rubber. The driver of the bus that was hit says an explosion blew out windows on the upper deck.
Thursday's incidents came as police continue to search for people connected to the July 7 bombings. That investigation has led to detentions in Egypt and Pakistan, and U.S. law enforcement agencies are also lending assistance.