Pakistan has denied reports that it opened fire first provoking the Nato air strike

Pakistan has denied reports that it opened fire first provoking the Nato air strike which killed 24 troops at a checkpoint on the Afghan border.

It follows claims by Afghan officials that Nato forces were retaliating for gunfire from the Pakistani side of the volatile border region on Saturday.

On Sunday Pakistan's army chief led mourners as those killed in the strike were buried at military headquarters.

Nato has apologised, calling it a "tragic unintended incident".

But the attack has heightened already tense relations between Pakistan, the US and Nato.

Pakistan reacted angrily to the attack, which took place at two remote border posts in Pakistan's tribal district of Mohmand in the early hours of Saturday morning. Several protests against Nato's actions have been held across the country.

Pakistan's Prime Minister Yousuf Raza Gilani called it a "grave infringement of Pakistan's sovereignty" and officials responded by cutting key supply Pakistani lines to Nato in Afghanistan.

'Not true'

But unnamed Afghan officials quoted in The Wall Street Journal said that Saturday's attack was called in to shield Nato and Afghan forces who were under fire while targeting Taliban fighters. One official quoted in the paper says that Kabul believes the fire came from an army base.

"This is not true. They are making up excuses. What are their losses, casualties?" Pakistani army spokesman Maj-Gen Athar Abbas said in a text message in response to the allegations.

Maj Gen Abbas has also said that the raid went on for more than an hour and continued even after local commanders contacted Nato telling them to stop the strike, according to the Associated Press news agency.

Pakistani officials have consistently maintained that there had been no militant activity in the area, and most of the Pakistani soldiers were asleep. They also said Nato had the grid references of the posts and therefore should not have fired