Pakistan ? Trucks bearing NATO supplies began flowing again Sunday across a critical border crossing into Afghanistan, opened a day earlier than expected by Pakistan and ending a blockade that had raised tensions between Washington and a key ally.

Pakistan had shut down the Torkham crossing along the Khyber Pass after a U.S. helicopter strike in the area killed two Pakistani soldiers 11 days ago.

Following an apology from top U.S. officials last week, Pakistan announced Saturday that Torkham would be reopened. The crossing is usually closed Sundays, however, and the U.S. had said it did not expect trucks to begin moving again until today.

It was not clear whether the decision to allow the vehicles through Sunday was a goodwill gesture by Islamabad, or a pragmatic move to relieve the backlog of vehicles that have been stranded along roads in Pakistan and left vulnerable to militant attacks.

During the blockade, about 150 trucks were destroyed and some drivers and police were injured in near-daily attacks which left drivers fearing for their lives and hurt trucking companies’ profits.

Though the U.S. has said the Torkham closure has not affected its ability to keep troops in Afghanistan supplied, the blockade was another irritant in its relationship with Pakistan.

At the heart of the tensions is Washington’s contention that Pakistan has been unwilling to go after Afghan Taliban militants in its lawless border region near Afghanistan, with whom it has strong historical ties and who generally focus their attacks on Western troops.

NATO has responded to Pakistan’s position by increasing its forces in key areas in Afghanistan near the border, including in Khost and Paktia provinces which abut Pakistan’s tribal region.