|The video at the centre of the army investigation purports to show Pakistani soldiers killing bound and blindfolded men
General Ashfaq Kayani, Pakistan's army chief, has ordered an investigation into a video posted on the internet showing men in Pakistani military fatigues shooting at a group of what the military said were civilians.
The video raised fresh questions about alleged extra-judicial killings by the army, while Pakistan faces mounting US pressure to crack down harder on suspected Pakistani fighters launching attacks on Western forces in Afghanistan.
Kayani said on Friday that part of the inquiry's mission was to determine whether those shown in uniform were actually soldiers.
An organisation called the International Pashtuns' Association posted the video on Facebook , saying that the incident took place during the military's crackdown on the Pakistani Taliban in the Swat valley in the summer of 2009.
US officials said that they had asked Pakistan for information about the video purporting to show Pakistani troops lined up in a firing squad shooting bound and blindfolded men in traditional Pakistani clothing.
Human rights groups say the video fits in with "credible allegations" they have received about the conduct of Pakistani troops. The Human Rights Commission of Pakistan said in June that 282 extra-judicial killings by the army had taken place in the Swat region in the past year.
Pakistan denied the allegations.
Amnesty International, the London-based rights campaigner, told Al Jazeera last week that while it could not confirm the authenticity of the video, it had "received credible reports of suspected insurgents being summarily executed by the Pakistani security forces in Pakistan's Swat valley".
"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," Kayani was quoted saying.
"(It is) unacceptable under any circumstances."
Kayani cautioned against "reaching hasty conclusion" as previously fighters had disguised themselves as soldiers during a number of attacks including one on military headquarters in the city of Rawalpindi last year.
If confirmed, the video could raise a legal headache for the US, which is bound by law not to give military aid and assistance to foreign armies found to have committed gross human rights violations.
Considered a crucial partner in the efforts to defeat the Taliban and al-Qaeda in Pakistan and Afghanistan, the Pakistani military has received $10bn from Washington since 2001, when the Taliban were overthrown by a US-led multinational force.
The US state department described the images as "horrifying," and has said that the issue will be raised with the Pakistani government by Anne Patterson, the US ambassador to Pakistan.