(CNN) -- The Torkham border crossing in Pakistan was opened for NATO supply convoy traffic Sunday morning, authorities told CNN.

Trucks are free to pass once they have cleared customs, said Amjad Ali, a constable for the Khyber Pakhtunkhwa province.

Pakistan closed the main land route for NATO supplies crossing from Pakistan to Afghanistan after U.S. helicopter strikes across the border killed two Pakistani soldiers.

A report from a NATO and Pakistan assessment team concluded that soldiers fired warning shots to let them know of their presence, but the helicopter crews assumed they were insurgents and fired the shots.

While the main route has been closed, at least seven attacks on convoys carrying supplies for NATO forces in Afghanistan have taken place in Pakistan. The convoys are generally operated by contracted Pakistani firms, using Pakistani trucks and drivers.

Since October 1, at least six people have been killed in attacks on supply vehicles.

The Pakistani Taliban has claimed responsibility for the most recent attack, which took place Saturday in Pakistan's western Baluchistan province.

Assailants attacked 28 oil tankers with a machine gun and rockets, said Meeran Bukhsh, a police official in the Bolan district, said. Police said the tankers caught fire, and two people were injured.

The attack was carried out by the Pakistani Taliban's special squad on U.S. assets in Pakistan -- particularly fuel trucks for NATO, Shakir Khan, the militants' spokesman said Saturday.

The special squad was purportedly founded in response to increased U.S. drone strikes.

"We are very proud of the performance of this squad as they have been able to successfully target NATO convoys all over Pakistan," Khan said.

A second supply route through Chaman in western Pakistan was open during the Torkham closure, but the Pakistani Taliban has threatened violence on any route used for NATO purposes.

Journalist Nasir Habib contributed to this report.