PESHAWAR, Pakistan - Pakistan closed the Khyber Pass border crossing with Afghanistan for 10 hours on Wednesday after mortar bombs landed in Pakistani territory from across the border, a Pakistani official said.

The Torkham crossing, through which thousands of vehicles pass every week, is the main trade link between the uneasy neighbours.

Exchanges of fire across the border, which Afghanistan has never recognised, are common. But an Afghan official denied that Afghan forces had fired into Pakistan.

Hundreds of vehicles that had been stuck on both sides began moving across the border on Wednesday afternoon after the crossing was reopened, Pakistani and Afghan officials said.

A Pakistani official said mortar bombs fired from Afghanistan landed in Pakistan territory. "The border is closed for investigation purposes," Mahmood Aslam Wazir, deputy district commissioner of the area on the Pakistani side, told Reuters at the time.

Wazir was not immediately available for comment on the findings of the investigation.

Afghanistan has for years accused Pakistan of supporting Taliban militants. Pakistan denies doing so and in turn accuses Afghanistan of supporting militants fighting the Pakistani government. Both countries are U.S. allies.

Attaullah Khogyani, spokesman for the governor of Afghanistan's Nangarhar province, suggested that Pakistani forces had fired the mortar bombs as an excuse to close the border.

"In the past, Pakistan has played the same game whenever they want to close the Torkham crossing," Khogyani told Reuters.

Pakistan was angered this week when Afghan President Ashraf Ghani condemned the arrest in Pakistan of a Pakistani ethnic Pashtun rights activist.

Pashtuns in Pakistan have been protesting recently against their government in a campaign for greater rights that many Pashtuns in Afghanistan support.

(Reporting by Jibran Ahmad in Peshawar and Abdul Qadir Sediqi in Kabul; Additional reporting by Ahmad Sultan in Nangarhar Writing by Gibran Peshimam Editing by Robert Birsel and Nick Macfie) ((GibranNaiyyar.Peshimam@thomsonreuters.com; +923018217003;))