Up to seven Afghan troops were killed in a border clash with Pakistani forces yesterday in the most serious incident in years between the uneasy neighbours who are officially partners in the US-led war on terrorism.

Pakistan Major-General Waheed Arshad said Afghan troops opened ?unprovoked firing? on five or six border posts in the Kurram tribal region in northwest Pakistan and that Pakistani paramilitary forces retaliated. ?We have reports that six to seven of their troops have been killed. Three of our soldiers have been wounded.?

Afghan army general Murad Ali Murad, who is based in the eastern Afghan province of Paktika, confirmed the clash and said there had been casualties on his side.

The clash erupted after Pakistani forces moved a border post toward the Afghan side in Zazai district, the Afghan general said. Afghan troops had been sent in to back up border police as the fighting escalated, he said.

Relations between the neighbours have deteriorated sharply over the past 18 months, largely over Afghan complaints that Pakistan is not doing enough to stop Taliban insurgents operating from the Pakistani side of the disputed border.

The clash comes two weeks after Afghan President Hamid Karzai and Pakistani President Pervez Musharraf met for the first time in months and agreed to step up security cooperation.

Afghanistan says a resurgent Taliban are operating from Pakistani sanctuaries. Pakistan, the main backer of the Taliban before the Sept. 11, 2001, attacks on the United States, denies and says that the root of the Taliban problem is in Afghanistan. Stung by accusations it is not doing enough to stop the insurgents, Pakistan has begun building a fence along parts of the border to stop militant infiltration. But Afghanistan opposes fencing a border it has never recognised.

Pakistan is also deeply suspicious of involvement of its old rival, India, in Afghanistan.