ISLAMABAD: Two men on a motorcycle threw a bomb at a truck carrying an excavating machine to NATO troops in Afghanistan, halting traffic yesterday along a supply route through Pakistan's southwest, officials said.

No one was injured in the blast near the Pakistani frontier town of Chaman, but the machine was damaged, area police chief Gul Mohammed said.

Meanwhile in the northwest, dozens of assailants opened fire at a university, killing three police officers and a security guard. A top government official said Taleban fighters detained 14 of the suspected attackers in Swat later yesterday.

US and NATO forces in Afghanistan rely heavily on two major supply routes running through Pakistan. The main one goes through the Khyber Pass in the northwest, and trucks that use it have frequently been attacked.

The smaller route through Chaman has attracted less attention from militants, but has not been exempt from violence.

Yesterday's attack happened as the driver awaited security clearance to cross into Afghanistan, Mohammed said. Police closed the crossing and began searching other vehicles, he said.

The gun attack occurred in Lower Dir, which borders Pakistan's militant-plagued tribal regions and is near the Swat Valley, where the government recently agreed to impose Shariah law to strike a peace deal with the Taleban.