Pakistani security officials examine a truck after a bomb attack in Chaman, a Pakistani town along Afghan border, Wednesday, March 18, 2009. -AP

ISLAMABAD Two men on a motorcycle threw a bomb at a truck carrying an excavating machine to Nato troops in Afghanistan, halting traffic on Wednesday along a supply route through Pakistans 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.

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.

Wednesdays 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 route was expected to reopen later Wednesday.