ISLAMABAD, April 20 (Reuters) - Pakistan said on Friday its troops had exchanged fire with an Afghan patrol a day earlier, but contradicted Kabul's account that Afghan troops were tearing down a fence Pakistan had put up on the disputed frontier.

The Pakistan military accused an Afghan patrol of opening fire without provocation on one of its border posts.

"Our forces retaliated and they ran away. There were no casualties," military spokesman Major-General Waheed Arshad said.

The Afghan Interior Ministry said on Thursday the gunbattle erupted after Pakistani troops opened fire on Afghan forces as they were removing a fence and mines laid by Pakistan.

Arshad denied Pakistani forces were fencing and mining the area.

"There was neither any fence there, nor did they tear one down. Nobody entered into Pakistani territory," he said.

Pakistan has put up fencing in selected parts of the long porous border to stop Taliban fighters sneaking across to attack Afghan, U.S. and NATO forces in Afghanistan.

Kabul opposes fencing because of a long-standing territorial dispute, and because it would penalise tribal communities with family on both sides of the Durand Line, named after the 19th Century colonial administrator who drew the border.

The clash happened on the border between Pakistan's South Waziristan tribal region and the Bermal district of Afghanistan's eastern province of Paktika.

Pakistan earlier this year announced plans to fence and mine parts of its 2,400 km (1,500 mile) border with Afghanistan after growing complaints by U.S. and Afghan officials that the Taliban militants were launching cross-border attacks from the safety of their sanctuaries on Pakistani soil.

It later decided against laying mines.

Pakistani officials said they planned to fence a 35 km (20 mile) stretch of the border in Waziristan, known as a hotbed of support for the militants.

(Additional reporting by Sayed Salahuddin)

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