Pakistani officials say at least four people have been killed and 19 wounded in northwest Pakistan when bombers attacked in a busy tunnel.

The officials said a truck packed with explosives blasted Kohat tunnel Friday night.

The tunnel connects the main northwestern city of Peshawar with the city of Kohat.

Kohat is a dangerous area close to the Afghan border where Taliban militants are engaged in a campaign of violence against government officials and security forces in Pakistan.

The tunnel has been a target for attacks in the past.