Rasmussen regrets deaths in airstrike as Pakistan announces review of ties with US and Nato

"I have written to the Prime Minister of Pakistan to make it clear that the deaths of Pakistani personnel are as unacceptable and deplorable as the deaths of Afghan and international personnel," he said. "This was a tragic unintended incident."

His statement comes as Pakistan conveyed its anger to the United States over the air strikes and ordered a full-scale review of its frosty alliance with the US and Nato.

Dossier: AfPak news and analysis

Earlier Sunday, Foreign Minister Hina Rabbani Khar telephoned US Secretary of State Hillary Clinton and conveyed a "deep sense of rage" as the military organised a joint funeral for the 24 troops who died.

Khar said attacks on military outposts were "totally unacceptable" as they contravened international law and violated Pakistani sovereignty - inflaming US-Pakistani relations still reeling from the May killing of Osama bin Laden.

An investigation of the incident is likely to ask whether Afghan and American troops on the Afghan side of the border were fired upon first - whether by insurgents or Pakistani military.

Pakistan on Saturday sealed its border with Afghanistan to NATO supplies - holding up convoys at the Torkham and Chaman crossings on the main overland US supply line.