Islamabad, Pakistan (CNN) -- Militants attacked two Afghanistan-bound tankers carrying fuel for NATO in northwest Pakistan on Monday, a police official told CNN.
Aslam Khan said at least six gunmen in two cars cut off the tankers and opened fire on a major highway near Pabbi, a town 120 kilometers northwest of Islamabad in the Khyber-Pakhtunkhwa province.
Two drivers and a passenger were injured, Khan said.
Khan said the tankers did not catch fire but were both leaking oil.
Since October 1, at least six attacks have been carried out on vehicles in Pakistan carrying fuel for NATO forces in Afghanistan. At least seven people have died from such attacks.
The tankers are operated by contracted Pakistani firms hired by NATO, using Pakistani equipment and drivers.
Journalist Nasir Habib contributed to this report.