Faisal Aziz

KARACHI, Apr 12 (Reuters) Pakistani troops patrolled the deserted streets of the southern city of Karachi today to stop any fresh violence after a suicide bomb blast at a Sunni Muslim prayer meeting killed at least 57 people.

Yesterday's strike by two suspected suicide bombers was the worst ever on Karachi, which has been plagued by sectarian violence and Islamist militant organisations angered by President Pervez Musharraf's support for the US-led war on terrorism.

Nobody had claimed responsibility for the attack and a Pakistani official said authorities were struggling to identify the group behind the blasts.

''Jihadis are all out against President Musharraf, so they may be involved,'' said Salahuddin Haider, spokesman of the provincial Sindh government.

Aside from homegrown Islamist groups, some of which have forged ties with al Qaeda, Haider said ethnic Baluch rebels from southwest Pakistan could also be on the list of suspects.

Indian and Afghan involvement could not be ruled out, although there was no evidence, he added.

Islamist militants, however, are more likely to use suicide bombers than groups driven by secular political motives, raising chances it was a sectarian attack.

''Our initial investigations suggest that there were at least two suicide bombers involved in the attack. We have found the body parts, including the heads, of the suspected attackers,'' Haider said.

The attackers struck while some 15,000 worshippers from a Sunni Muslim organisation, Jamaat-e-Ahle Sunnat, had gathered for prayers in a city park to mark the anniversary of Prophet Mohammad's birth.

Among the dead were several leaders of Jamaat-e-Ahle Sunnat, which has hundreds of thousands of followers among Pakistan's dominant Barelvi sect of Sunni Muslims, raising fears of a violent backlash.

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