Twenty-one tribal policemen believed to have been kidnapped by the Taliban were found shot dead in Pakistan’s troubled northwest tribal region early Sunday, government officials said.

Officials found the bodies shortly after midnight in the Jabai area of Frontier Region Peshawar after being notified by one policeman who escaped, said Naveed Akbar Khan, a top political official in the area.

Another policeman was found seriously wounded, said Khan.

The 23 policemen went missing before dawn Thursday when militants armed with rocket-propelled grenades and automatic weapons attacked two posts in Frontier Region Peshawar.

Two policemen were also killed in the attacks. Militants lined the policemen up on a cricket pitch late Saturday night and gunned them down, said another local official who spoke on condition of anonymity because he was not authorized to talk to the media.

No group has claimed responsibility for the attack, but suspicion fell on the Pakistani Taliban, who have been waging a bloody insurgency against the government for the past few years.

The tribal region is the main sanctuary for the Taliban in Pakistan. On Saturday, an explosion ripped through a passenger bus at a terminal in the southern city of Karachi, killing six people and wounding 52 others, some of whom were in critical condition, said Seemi Jamali, a doctor at the hospital where the victims were being treated.

Police were trying to determine whether the blast, which reduced the bus to a charred skeleton, was caused by a bomb or a gas canister that exploded, said police spokesman Imran Shaukat.

Many buses in Pakistan run on natural gas. Karachi has a long history of political, ethnic and sectarian violence. It is also believed to be home to many Taliban militants who have fled U.S. drone attacks and Pakistani army operations in the country’s northwest.

Also on Saturday, a government official said authorities are investigating allegations that cough syrup has killed 33 people over the past three days in eastern Pakistan, the second time in recent months medicine is suspected of causing multiple deaths.

Associated Press writers Adil Jawad in Karachi, Pakistan, and Zaheer Babar in Lahore, Pakistan, contributed to this report.

- AP