YAKKAGHUND: Nato helicopters attacked a military checkpoint in northwest Pakistan on Saturday, killing up to 28 troops and prompting Pakistan to shut the vital supply route for Nato troops fighting in Afghanistan, Pakistani officials said.

The Foreign Office condemned Saturday's attack.

“Prime Minister Yusuf Raza Gilani has condemned in the strongest terms the Nato/Isaf attack on the Pakistani post,” ministry spokeswoman Tehmina Janjua said in a statement.

“On his direction, the matter is being taken (up) by the foreign ministry in the strongest terms with Nato and the US.”

Two military officials said that up to 28 troops had been killed and 11 wounded in the attack on the Salala checkpoint, about 2.5 kilometres from the Afghan border.

The attack took place around 2 a.m. in the Baizai area of Mohmand, where Pakistani troops are fighting Taliban militants.

A senior Pakistani military officer said efforts were under way to bring the bodies of the slain soldiers to Ghalanai, the headquarters of Mohmand tribal region.

“The latest attack by Nato forces on our post will have serious repercussions as they without any reasons attacked on our post and killed soldiers asleep,” he said, requesting anonymity because he was not authorised to talk to the media.

About 40 Pakistani army troops were stationed at the outpost, military sources said.

Two officers were reported among the dead.

Nato supply trucks and fuel tankers bound for Afghanistan were stopped at Jamrud town in the Khyber tribal region near the city of Peshawar hours after the raid, officials said.

“We have halted the supplies and some 40 tankers and trucks have been returned from the check post in Jamrud,” Mutahir Zeb, a senior government official, told Reuters.

Another official said the supplies had been stopped for security reasons.

“There is possibility of attacks on Nato supplies passing through the volatile Khyber tribal region, therefore we sent them back towards Peshawar to remain safe,” he said.

Pakistan is a vital land route for 49 per cent of Nato's supplies to its troops in Afghanistan, a Nato spokesman said.

A spokesman for the Nato-led International Security Assistance Force in Kabul said the coalition there was aware of “an incident” and was gathering more information.

The Afghanistan-Pakistan border is often poorly marked, and differs between maps by up to five miles in some places.

The incident occurred a day after US General John Allen met Pakistani Army Chief of Army Staff General Ashfaq Pervez Kayani to discuss border control and enhanced cooperation.

This raid is the largest and most serious incident of its kind. A similar incident on September 30, 2010, which killed two Pakistani troops, led to the closure of one of Nato's supply routes through Pakistan for 10 days.

Nato apologised for that incident, which it said happened when Nato gunships mistook warning shots by the Pakistani forces for a militant attack.