At least 25 Pakistani troops have been killed in a clash that is still ongoing 24 hours after militants crossed the Afghan border. About 200 insurgents, whom police say were wearing military uniform, ambushed a security checkpoint in Upper Dir, outside Pakistan's tribal areas. Officials said army support had arrived at the remote checkpoint. Upper Dir, which lies just outside Pakistan's volatile tribal areas, is regularly targeted by insurgents. The militants began their raid on Wednesday on the town of Shaltalo in a remote, mountainous corner of Upper Dir district, near the border with Kunar province of Afghanistan. At least 13 Pakistani security troops were killed in a similar cross-border raid by Taliban in the neighbouring Lower Dir district two months ago.