A truck packed with explosives blew up in a crowded market in northwestern Pakistan on Thursday, killing 11 people, as security concerns led officials to temporarily close a supply route to NATO troops in Afghanistan.

The blast in Salarzai town in the Bajur tribal area near the Afghan border also wounded nearly two dozen people, some of them critically, and damaged several vehicles and shops, said Jehangir Azam, a local government administrator.

It's unclear whether the attack was a suicide bombing, or if the explosives were detonated by remote control, he added. No group has claimed responsibility for the attack.

A shop owner who was injured in the explosion, Sher Mohammed, was sitting in his store when he saw a pickup truck enter the bazaar. Minutes later he heard a loud detonation.

"Something hurt my arm, chest and leg, and I fell down," said Mohammed. "When I opened my eyes, I found myself on this hospital bed."