Prior to Tuesday's train explosions in Mumbai, India, transit systems in major metropolitan centers in Europe and Asia have been the targets of terrorist groups. Here's a look at some of the most recent attacks on mass-transit systems:

—On March 20, 1995, Tokyo subway riders, at the height of the morning rush hour, were targeted in a deadly nerve-gas attack by a doomsday cult. The attack killed a dozen people, including two frontline employees and injured approximately 5,000 more.

—On Oct. 17, 1995, eight people died and more than 200 were injured when a terrorist detonated a bomb on the Paris Metro. Police later found the remains of a 6-pound cooking-gas canister that had been filled with explosives and screws — to serve as shrapnel.

—On Feb. 6, 2004, an explosion in a Moscow Metro rail car killed 39 people and wounded 129 others during the morning rush hour. The explosive device was thought to have been stored in a backpack or briefcase.

—On March 11, 2004, a coordinated series of 10 explosions aboard four packed commuter trains in Madrid killed 191 people and injured more than 1,500 others. The attacks were carried out by terrorists boarding the system at outlying stations, deploying their device laden packages on the trains, and exiting before the predetermined time of detonation.

—On July 7, 2005, the London transit system was attacked by four homicide bombers. Three of the devices were detonated on separate trains deep in the Tube. The fourth was detonated more than 30 minutes later on a double-decker bus. In total 56 people, including the four attackers, were killed and 700 others were injured.

—On July 21, 2005, two weeks after the London bombings, another four attacks were attempted on London's Underground. Only one person was injured, but the system, and to a great extent London, were crippled for a considerable amount of time.

Source: Statement of Chris Kozub, associate director, National Transit Institute, Committee on House Homeland Security Subcommittee on Emergency Preparedness, Science, and Technology, July 26, 2005.