Scrambling to track down militants responsible for the devastating suicide bombing of the Marriott hotel in Islamabad [Images], Pakistani security forces on Monday arrested three men during an operation from Kharian city of the Punjab province.

Among those arrested was Qari Muhammad Ali, imam of the main Jamia mosque in Kharian, Dawn News channel reported.

There was also no official word on the arrests and no further details were available. The security forces have launched a massive manhunt in Islamabad as well as adjoining provinces to trace militant cells responsible for the suicide bombing, which killed 53 people, including two US marines and the Czech ambassador to the country.

As part of the drive, investigators are looking into the possibilities that the bombers constructed a 600-kg bomb in a safe house in Islamabad itself, as transporting such a heavy load could not pass the numerous checks on the highway leading to the capital.

Reports said Pakistani authorities had launched a crackdown over the weekend on leaders and members of banned organisations. In another operation at Gujranwala in Punjab late on Sunday night, two alleged terrorists were arrested by security forces.

Local residents and witnesses said security personnel raided Zubeida Hanifia mosque and arrested its imam, Qari Muhammad Ashraf, and Al Qaida suspect Jamshed Mursalin, who was believed to be involved in a suicide attack in Rawalpindi on former president Pervez Musharraf [Images].

A suicide bomber rammed a truck packed with 600 kg of explosives into the main gate of the Marriott on Saturday, causing widespread devastation.

The Czech ambassador and two US Marines were among the 53 people killed in the attack, described by officials as the biggest ever bombing in Pakistan's history.