The authorities said on Thursday they suspected a network of extremists, possibly aided by al Qaeda, were behind a double car bomb attack near Pakistan American Cultural Centre (PACC) here in which a policeman was killed and 32 people injured.
"Al Qaeda may have a role," Information Minister Sheikh Rashid told AFP.
"Such an organised attack cannot be just by local people. The attackers were real experts and operated in a very technical way."
Police cast suspicion on supporters of Harkatul Mujahideen al-Alami, a gang who unsuccessfully tried to blow up President Musharraf's motorcade in Karachi in April 2002 and detonated a car bomb outside the US consulate two months later, killing 12 persons.
"We strongly suspect al-Alami," senior police investigator Manzoor Mughal told AFP.
Followers may have retaliated for the arrests, days before the attack, of seven members, including suspected key terror operative Kamran Atif, Mughal said.
Police issued sketches of two suspects who had stolen at gunpoint one of the cars from a nearby market less than two hours before the attack.
One of the men was bearded and the other had a thin moustache.
"They planted the lethal explosives in the car and parked it" half an hour before the blast, police investigator Fayaz Leghari told AFP.
President Musharraf said such attacks were easily executed due to the availability of explosives and suicide bombers.