KARACHI: A suicide bomber blew up a Shi'ite Muslim procession in Pakistan's commercial capital Karachi yesterday, killing at least 25 people, in an attack that underscored multiple security challenges facing the US ally.

The assault on the religious march, the third in Pakistan's biggest city in as many days, was launched during a difficult time for the government of President Asif Ali Zardari.

Al-Qaida-linked Taliban militants have killed hundreds of people in bombing in retaliation for a major government offensive in mid-October.