ISLAMABAD » Pakistan’s army chief ordered an inquiry Friday into video clips that show men in soldiers’ uniforms gunning down a group of bound and blindfolded detainees. The footage has raised concern over possible extrajudicial killings by a military that receives billions in U.S. aid.

The two clips were apparently shot by cell phones and have been circulating on the Internet. The footage is grainy and shows no time stamps, and part of the army inquiry’s mission is to determine whether those shown in uniform were actually soldiers, Gen. Ashfaq Parvez Kayani’s statement said.

"It is not expected of a professional army to engage in excesses against the people whom it is trying to guard against the scourge of terrorism," the general said, though he cautioned that militants had in the past posed as soldiers.

It was unclear where the clips were first posted. The SITE Intelligence Group, a U.S.-based organization that monitors militant websites, reported about two weeks ago they had appeared on an extremist site. The group said they were posted by someone who claimed the footage was from Pakistan’s Swat Valley, the scene of a major army offensive against Taliban militants in 2009.

The Pakistani army has been accused of carrying out extrajudicial killings in Swat ever since launching the offensive in May 2009 — allegations it denies.

The accusations have concerned American officials who have helped Pakistan gain training and money to improve its fight against al-Qaida and the Taliban. U.S. law forbids aid to foreign militaries if they are found to be committing gross violations of human rights.

U.S. Ambassador Anne Patterson had spoken to Kayani about the videos when they surfaced and American officials were pleased to learn of the probe, embassy spokesman Richard Snelsire said.

The longer clip lasts 5 minutes and 39 seconds and shows what appears to be a group of Pakistani soldiers, fully armed and in uniform, guiding the blindfolded men to a wooded area in front of a wall and lining them up next to one another. They are then shot.

A voice is heard saying "finish them one by one." A soldier then walks over to the men and shoots them again.

The second clip last 53 seconds and shows only the executions.

Kayani’s statement Friday said an inquiry board would be set up headed by a major general and two to three senior officers who have experience investigating such incidents. It did not give a deadline for the investigation.

Pakistan is of such strategic importance to the war effort in Afghanistan that U.S. officials may hesitate to suspend military aid over allegations of human rights violations.

To maintain Pakistan’s cooperation in the fight against the Soviets in Afghanistan in the 1980s, the U.S. routinely waived laws aimed at preventing aid to a country making nuclear weapons. Pakistan tested its first nuclear bomb in 1998.

Rights activists said past army inquiries into alleged extrajudicial killings and abuses had held no one accountable.

"We hope that this will in fact be a meaningful inquiry and not a sham perpetrated to assuage international concerns," Ali Dayan Hasan of Human Rights Watch said of the latest probe.

The footage has received very little, if any, media coverage in Pakistan. The army is the country’s most powerful institution, and newspapers and TV stations are very careful about how they cover its activities.

Neverthless, the clips could hurt efforts by the army to win public backing for its campaign against al-Qaida and the Taliban in Swat and other parts of the northwest close to the Afghan border. Journalists have limited access to most of the conflict zones, making it difficult to document the military’s activities in full.

In October, video apparently showing Pakistani soldiers beating men detained in anti-militant operations in the northwest surfaced on Facebook and YouTube. The army said it would investigate, but has not publicly released the results of any probe.