Col Abdul Hanan, the acting provincial police chief in the eastern Khost province, says the fighting broke out today and is still underway. He was not immediately able to confirm reports of casualties.
The two countries are separated by the 2,400-kilometer (1,500-mile) Durand Line, which was drawn by British rulers in 1896.
The two US allies routinely accuse each other of failing to crack down on militants who operate along the porous border.
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