BAGHDAD/KERBALA, Iraq (Reuters) - Blasts tore through Shi'ites marking their holiest day in Baghdad and Kerbala Tuesday, killing at least 124 people on Iraq (news - web sites)'s bloodiest day since Saddam Hussein (news - web sites)'s fall.

Furious leaders of the country's 60 percent Shi'ite majority branded the attacks an attempt to ignite civil war.

Polish troops in Kerbala and U.S. soldiers in Baghdad said the blasts were caused by mortars which landed among huge crowds of Shi'ites in near-simultaneous attacks on the two cities.

The U.S. military said last month it had evidence al Qaeda guerrillas were planning to attack Shi'ites to spark sectarian violence.

At least five explosions shook Kerbala, a holy city where more than two million Shi'ites from Iraq, Iran and further afield had gathered. Colonel Raed Nabil, the city police chief, said at least 70 Iraqis and Iranians were killed in the attacks.

In Baghdad, four blasts hit the holiest Shi'ite mosque, the Kadhimiya mosque in the north of the capital. The health minister said at least 54 people were killed but the number of scattered body parts hampered collating a death toll.

One medic said the Baghdad toll could be more than 75.

In a separate attack in Baghdad, guerrillas threw a bomb at a U.S. military vehicle early Tuesday, killing one American soldier and seriously wounding another, the army said...