CHAMAN, Pakistan, Aug 31 (Reuters) - Suspected Taliban militants set fire to 18 container trucks carrying supplies for Western forces in neighbouring Afghanistan in the Pakistani border town of Chaman, police said on Monday.

Some 300 trucks were parked near the border crossing in the country's southwest, as the border had been closed by Pakistani authorities since Friday in a row with their Afghan counterparts over the checking of trucks coming from landlocked Afghanistan.

"The attackers probably had planted explosives under one of the oil tankers which went off, setting others on fire," Abdul Rauf, a senior border police official, told Reuters. "Eighteen trucks have completely been destroyed."

Witnesses, however, said the militants lobbed a grenade onto the trucks, setting them on fire.

"They came on motorcycles. They first opened fire with guns, then threw a rocket-propelled grenade towards our vehicles and ran away," Akhtar Mohammad Niazi, a driver, told Reuters.

Rauf said the authorities had reopened the border crossing after the incident, which took place late on Sunday.

"There's a constant threat to NATO supplies so we have decided to reopen the border after the last night attack," he added.

Chaman is one of the two Pakistani border crossings used for the transport of food and fuel supplies to Western nations battling a resurgent Taliban in Afghanistan.

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.

Most of these supplies are trucked through the Khyber Pass, to the northwest, to eastern Afghanistan, but that route has been plagued by militant attacks since last year.

In the past, the route through Chaman, in Baluchistan province, has been largely free of attacks, at least on the Pakistani side.

The attacks, especially in the Khyber region have forced NATO to look for alternative routes, including through Central Asia into northern Afghanistan.