The victims were Shiite Muslims, a minority in Pakistan that is frequently targeted by extremists from the majority Sunni community, said lawmaker Abdul Sattar. The gunmen spared several dozen other people in the four-bus convoy. A spokesman for a faction of the Pakistani Taleban, a Sunni militant group, claimed responsibility for the killings.
The incident in the remote Kohistan region was the latest in a spasm of violence in the country in recent weeks that has demonstrated the resilience of militant networks, including groups allied to Al-Qaeda. The US has tried to support Pakistani security forces in the fight against the extremists, but strained relations between the two nations hamper cooperation.
The bloody attack took place in the mountainous village of Harban Nala, which is some 210 miles (340 km) north of the capital Islamabad. The area, part of the famed Silk Road linking northern Pakistan to China, is populated by Sunni tribes.
Police officer Mohammad Azhar said the buses were traveling from Rawalpindi to Gilgit when the gunmen attacked.
Sattar, the lawmaker, said eight gunmen were involved in the ambush, and all were wearing military uniforms, presumably to make it easier to stop the buses. He said the attackers ordered the passengers to produce their identity cards before ordering the 16 off the bus and shooting them.
Officials initially said 18 people had been killed and that just one bus was involved.
Sattar and Sher Khan, an official at the Rawalpindi bus station, said attacks had been feared on travelers after an incident last month in which an unknown number of Sunnis were killed in the Gilgit region. Khan said buses were traveling in convoy as a security measure.
Sunni extremists allied to or inspired by Al-Qaeda and the Taleban routinely attack government and security force targets, as well as religious minorities and other Muslim sects they consider infidels. Most of the violence has been in the northwest, close to Afghanistan, though sectarian attacks happen across the country with some regularity.
Many thousands have been killed in the last five years, and attacks on Shiites — targeted purely because of their sect — have been some of the bloodiest.
The Jandullah faction of the Pakistani Taleban — one of the country's deadliest and best organized militant groups — claimed responsibility.
"They were Shiite infidels and our mujahedeen shot them dead one by one after bringing them down from a bus," said Ahmed Marwat, a purported commander, who called an Associated Press reporter from an undisclosed location.
Also Tuesday, gunmen on a motorcycle shot dead a Chinese woman and local man in a market in the northwestern city of Peshawar, police officer Tahir Ayub Khan said. He said officers were looking into the motive of the attack.
