KARACHI, Pakistan (AP) -- A parked car bomb targeting Pakistan's elite police commando force killed at least 12 officers and wounded 55 people in the southern city of Karachi on Thursday, police said, raising doubts about the success of an ongoing peace process with the Pakistani Taliban.
Hours after the attack, Taliban spokesman Shahidullah Shahid claimed responsibility for the bombing, which took place as a bus with the officers was leaving a training complex.
As the bus drove by a parked van, the van exploded, said police officer Rao Anwaar. Karachi police chief Shahid Hayat said the initial investigation suggested there was a remotely-detonated bomb on the van.
Nearly 50 officers on board the bus were from the Rapid Response Force, a special anti-terrorist police squad, Anwaar said. Most of the wounded also were officers on the bus.
Pakistani TV channels showed the blast scene littered with broken glass and pieces of vehicles scattered around.
The wounded were rushed to nearby hospitals, and 12 of them were in critical condition, said Dr. Seemi Jamali at the city's Jinnah Hospital.
Thursday's attack took place in the port city of Karachi, which has long been a center of ethnic, political, militant and sectarian violence.
Shahid, the Taliban spokesman, said the militants carried out the bombing to avenge the killing of their associates at the hands of police and paramilitary rangers. He said that until there was a formal ceasefire in place with the government, the Taliban would continue such attacks.
The assault is the latest in a series of attacks at a time when the Pakistani government is trying to strike a peace deal with local Taliban militants fighting in the country's northwest to end the violence that has killed thousands of security forces personnel, government officials, political workers and civilians in recent years.
Militants killed nine members of an anti-Taliban militia on Wednesday in Pakistan's northwestern city of Peshawar, a day after assailants threw hand grenades inside a cinema, killing 13 in the city.
The Pakistani Taliban have been waging a bloody war against the government in a bid to overthrow the authorities and enforce their harsh brand of Islamic Shariah law.
The Pakistani Taliban, formally called Tehrik-e-Taliban Pakistan, are separate from the Taliban fighting NATO-forces in neighboring Afghanistan. Although the two groups share similar ideology, the Pakistani Taliban have focused their fight against the Pakistani government.
Pakistani Prime Minister Nawaz Sharif has made negotiating with the militants a centerpiece of his new government elected last May.
After some initial stumbles, the government's efforts have picked up steam in recent weeks with both sides naming people to represent them in the talks.
Maulana Samiul Haq, who heads the Taliban's negotiating team, said both the militants and the government have recommended a cease-fire as a confidence-building measure.
The two teams were scheduled to meet again on Thursday.
Critics say the militants have used such peace deals to gain time to strengthen themselves and regroup.
Associated Press writer Riaz Khan in Peshawar contributed to this report.