Islamabad, Pakistan (CNN) -- A planted bomb caused a blast that killed at least 18 people traveling in a passenger van in northwest Pakistan Monday, police said.
Around 10 kilograms (22 pounds) of explosives were planted inside the van, police official Islam Ud-Din said. He said an earlier police report indicating that the explosion was caused by a head-on crash between two passenger vans was inaccurate.
Earlier Monday, police said 11 people were injured in the blast.
The explosion went off when the van was traveling from the district of Hangu to the bordering district of Kohat, Ud-Din said. It also damaged a second passenger van that was traveling nearby, he said.
It was not immediately clear why the passenger van was targeted, but the district of Hangu sits in a region plagued by sectarian violence between Sunnis and Shias.
Last March, a suicide bomber attacked a convoy of vehicles carrying Shia passengers in Hangu, and a suicide car bomb rammed into a Shia hospital there in December.