PESHAWAR, Pakistan — Pakistani and Afghan forces exchanged heavy gunfire on Sunday and Monday in an unusually serious escalation of tensions at the border, leaving at least 13 people wounded on the Pakistani side and killing at least one Afghan police officer, according to the police and military officials in both countries.

The fighting, which began on Sunday night and resumed Monday, forced the closing of the Torkham border crossing, the busiest between the two countries.

The escalation followed the closing of the Torkham crossing last month after Afghan border security guards objected to the construction of a gate on the Pakistani side. That objection also apparently contributed to the conflict on Sunday, according to official accounts from both sides.

The border remained closed for five days last month but was reopened after a meeting between the Afghan ambassador to Pakistan, Hazrat Omar Zakhilwal, and Pakistan’s army chief, Gen. Raheel Sharif.