By Aamir Latif

KARACHI

 Pakistan police have arrested four al-Qaeda suspects allegedly involved in last week's deadly gun attack on a bus that killed 45 members of the tiny Shia-Ismaili community in southern port city of Karachi.

The suspects were arrested in a joint operation of intelligence agencies, and the counter terrorism of Karachi police from different parts of Karachi, Raja Umer Khitab, the head of the counter terrorism bureau told reporters on Tuesday.

Khitab said the bus attack was an act of al-Qaeda's subcontinent branch.

A brother of one of the suspects was also killed in a clash with police earlier this month in Karachi, he added.

Heavily armed militants intercepted a bus carrying Shia-Ismailis in the outskirts of Karachi last week, and shot 45 people including 16 women dead from close range.

This marks the second deadliest attack after a gun-and-bomb attack on an army-run school in Peshawar that killed over 140 people, mostly children in December last year.