PESHAWAR, Pakistan, Jan. 17 (UPI) -- An explosion tore through a passenger bus in Pakistan's northwest region Monday, killing at least 18 people, police said.
The blast occurred as the bus traveled on Hangu road in Kohat in Khyber-Pakhtunkhwa province, formerly called the North-West Frontier province.
Geo News and CNN reported the death toll was 18.
At least nine other people were injured in the explosion near the border with Afghanistan.
It was not clear if the explosion was the work of militants or was caused by a natural gas container.
Geo News quoted Kohat police official Masood Afridi as saying the nature of the blast was not known. "Terrorism cannot be ruled out," he said.
The province has been the scene of militant violence in recent weeks. On Thursday, three people died in two separate attacks in Bannu district.
Those attacks came a day after a suicide bomber rammed his explosives-laden vehicle into a police station, killing at least 18 people.
Pakistan's northwest region is next to the country's tribal areas, which U.S. intelligence officials say they suspect have become a haven for Taliban and al-Qaida leaders to launch attacks on U.S. and NATO forces in Afghanistan.
Scores of suspected U.S. drone missile strikes have targeted militants in the tribal areas.