Islamabad, Pakistan (CNN) -- Four people were killed in northwest Pakistan Friday when more than two dozen armed attackers blew up oil tankers carrying fuel for NATO troops in Afghanistan, police said.
Militants wielding automatic weapons first killed two guards at the main gate of a terminal on the outskirts of Peshawar city, where 18 tankers were parked, senior police official Imtiaz Shah said.
The attackers then planted explosive devices under a dozen tankers, he said, and killed two drivers who were sleeping in the terminal.
About 15 tankers were damaged after catching fire in the blasts, which occurred around 2 a.m. Friday, Shah said.
Two other drivers in the terminal were injured, Shah said.
There was no immediate claim of responsibility, but militants in the region have frequently targeted Pakistani security forces and supply trucks headed for Afghanistan in an effort to undermine U.S. and NATO efforts there.
More than half of the supplies for NATO forces in Afghanistan travels through Pakistan.