The United States and Pakistan will conduct a joint investigation of an attack along the Afghan border earlier this week that Pakistani officials said killed 11 of their soldiers, a U.S. spokesman said Friday.

Richard Boucher, a U.S. State Department official, said the joint probe was to ensure that such incidents didn't happen again between the two close allies.

Pakistan says a U.S. air-strike killed 11 soldiers and wounded at least 10 others at a remote frontier post late Tuesday but American military officials have only said said U.S.-led forces called in air support to repel an attack in the area by militants.

Pakistan has lodged a protest with NATO over the strike.

Officials in Foreign Minister Shah Mehmood Qureshi's office said he conveyed the protest to NATO Secretary General Jaap de Hoop Scheffer during a conference on Afghan reconstruction in Paris.

A ministry statement released late Thursday said Qureshi called the strike "unprovoked and senseless" and a "blatant and wilful negation of the sacrifices Pakistan has made in the war against terrorism."

The ministry said that de Hoop Scheffer expressed regret, but NATO has not made any public comment on the protest.

Coalition video shows explosions

A video of the incident released by the Pentagon shows blurred, grainy images of men firing rifles and rocket-propelled grenades in rugged mountainous terrain.

In the final sequence, four explosions can be seen and a narrator says these were precision attacks on anti-Afghan militants. The commentator asserts that no military structures or posts are in the impact area.

A U.S. military statement said the operation was co-ordinated with Pakistani officers.

For its part, the Pakistan army said the U.S. strike "hit[s] at the very basis of co-operation" between Pakistan and the United States in the campaign against the Taliban and al-Qaeda forces in Afghanistan.

Both countries have since said their joint work against Islamist militants will continue, despite the border incident.

New government plays down U.S. alliance

Since the attacks of Sept. 11, 2001, the two countries have been close allies against Islamist militants, many of whom are based in the rugged, tribal territories along the northwest Pakistani frontier with Afghanistan.

Pakistan's newly elected government has tried to play down an increasingly unpopular close relationship with Washington and has negotiated ceasefires with border-based militants, over strong objections from U.S. and Afghan officials.

Taliban supporters in the frontier area have also been blamed for campaigns of violence in Pakistan, including the assassination of former leader Benazir Bhutto late last year.

The new government in Islamabad says agreements with militants are intended to contain those attacks, not destabilize Afghanistan.

But NATO commanders say Pakistani territory is a staging area for insurgents, and easing the pressure on militants in the border area only exacerbates the dangers faced by alliance troops.