Iraqi authorities say attacks on Shi'ite pilgrims have killed at least 63 religious devotees on their way to commemorate one of Shi'ite Islam's holiest gatherings.

A bomb blast in southern Baghdad Monday killed at least four pilgrims and wounded 15 others.

Sunday, a suicidebomber killed 56 pilgrims who had stopped for refreshments in Iskandariyah, south of the capital.

Earlier Sunday in Baghdad, attackers killed at least three Shi'ite pilgrims and wounded nearly 40 others.

The U.S. Embassy and U.S. military in Iraq blamed al-Qaida in Iraq for Sunday's attacks.

The pilgrims are traveling to the central city of Karbala to commemorate Arbaeen, during which believers mark the 40th day following the anniversary of the martyrdom 13 centuries ago of the Prophet Muhammad's grandson.

In a separate attack today, Iraqi police say a suicidebomber in a wheelchair blew himself up in a police building north of Baghdad. At least one senior police officer was killed.

Authorities say the apparently disabled man entered the building and asked to meet with the deputy police chief Major-General Abdul-Jabbar Rabee Muttar. When the police official approached, the bomber detonated his explosives, killing the deputy chief and wounding two other police officers.