A truck packed with explosives exploded in a crowded market in northwestern Pakistan close to the Afghan border on Thursday, killing 11 people, a government official said.

The blast in Salarzai town in the Bajur tribal area 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 it was a suicide bombing, or if the explosives were detonated by remote control, said Mr. Azam.

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

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

Mr. Mohammed cursed the attackers, saying “I don’t know why we have been targeted.”

No group has claimed responsibility for the attack.

The Pakistani Taliban have a strong presence in Bajur, but the group’s spokesman, Ahsanullah Ahsan, denied they were behind the bombing. The group often denies involvement in bombings with significant civilian casualties.

The Army has carried out several offensives against militants in Bajur, but they continue to stage attacks.

Also on Thursday, Pakistan temporarily closed one of the two crossings used by NATO to ship troop supplies into Afghanistan because of security concerns, said Bakhtiar Khan, a local government official.

The decision to close the Torkham crossing in the northwest Khyber tribal area followed an attack in the area on Tuesday in which gunmen opened fire on a convoy carrying NATO troop supplies, killing a driver and wounding two other people.

The crossing could remain closed for several days as officials work with Pakistan’s paramilitary Frontier Corps to come up with an adequate security plan, said Mr. Khan.

The other crossing used by NATO convoys, Chaman in southwest Baluchistan province, remains open, said customs official Mohammed Tariq.

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