LANDI KOTAL, Pakistan (Reuters) -- Militants set off a roadside bomb in northwest Pakistan as trucks supplying Western forces in Afghanistan were passing by, wounding three people, a government official and witnesses have said.
It was the second attack in two days on supplies for Western forces heading through Pakistan's Khyber Pass, a vital supply route into landlocked Afghanistan.
The convoy was bombed in the Landi Kotal area, 30 kilometers west of the main northwest Pakistani city of Peshawar.
"The bomb was placed under a bridge and went off when the first vehicle of the convoy was crossing, wounding three people," a district government official said.
A taxi driver in the area said two truck drivers and a driver's assistant had been wounded and the convoy was stuck because the bridge had been damaged.
Al-Qaeda and Taliban militants have stepped up attacks in Pakistan, especially in the northwest where security forces are trying to eliminate militant strongholds from where they orchestrate violence in Pakistan and Afghanistan.
On December 1, two truck drivers taking supplies to Afghanistan were killed in a grenade and gun attack near Peshawar.
The trucks were parked at a terminal on the outskirts of Peshawar when militants fired rocket-propelled grenades at them, setting several of them on fire.
The U.S. military sends 75 percent of supplies for the Afghan war through or over Pakistan, including 40 percent of the fuel for its troops, the U.S. Defense Department says.
There are only two major routes into Afghanistan from the Pakistani port of Karachi, one through the Khyber Pass and the other through the town of Chaman to the southwest, the gateway to the southern Afghan city of Kandahar.
Pakistani authorities halted movement of supplies through the Khyber Pass for a week in November after militants hijacked 13 trucks carrying Western forces' supplies.