By Faisal Aziz
KARACHI (Reuters) - A suicide bomber attacked a Shi'ite Muslim procession in Pakistan's commercial capital Karachi on Monday, killing at least 15 people, police said.
The attack on a Shi'ite march, the third in Pakistan's biggest city in as many days, underscored the multiple security challenges facing the country.
The nuclear-armed U.S. ally is struggling against al Qaeda-linked militants and is under pressure from Washington to help stabilise neighbouring Afghanistan, where a Taliban insurgency is raging.
The bomb exploded at the end of a procession for Ashura, the Shi'ite calendar's biggest event.
Television pictures showed a big cloud of smoke over the scene and reporters said angry worshippers attacked journalists.
Provincial interior secretary, Arif Ali Khan, told Reuters: "It was a suicide attack and took place at one of the camps set up along the roadside to help the mourners."
Karachi police chief Waseem Ahmed said 15 people had been killed. The severed head of the suicide bomber had been found, he said. He appealed for calm.
Ashura falls on the 10th day of a 40-day mourning period during the Islamic calendar's first month, Moharram, which commemorates the death of Imam Hussein, a grandson of the Prophet Mohammad, who was killed in battle in A.D. 680 in the Iraqi city of Kerbala.
Processions by minority Shi'ite Muslims are often attacked by majority Sunni Muslim militants.
(Writing by Michael Georgy; Editing by Alex Richardson)
