KABUL, Afghanistan — Pakistan has kept its border crossings with Afghanistan sealed for more than two weeks, with thousands of Afghan visitors stranded in Pakistan and traders unable to move their vegetables and fruit across.

After a suicide bombing at a shrine in Pakistan’s Sindh Province on Feb. 16, which killed more than 80 people, the Pakistani military shut its borders with Afghanistan, saying the terrorists behind the attack had sanctuaries in the country. It also carried out shelling into Afghanistan.

Omar Zakhilwal, Afghanistan’s ambassador to Pakistan, said Sunday that if the border did not open soon, his government would be forced to airlift its stranded citizens, which could be a new low in the relationship between the neighboring countries.

Their 1,600-mile border has long been a contentious issue. Ever since the fall of the Taliban government in 2001, Afghan and Western officials have said that the Afghan insurgency’s leadership maintains havens in Pakistan, particularly in the city of Quetta. The free movement across the border has helped the militants avoid defeat in a 15-year war led by the United States.