WASHINGTON (Reuters) - Classified U.S. military video showing a 2007 attack by Apache helicopters that killed a dozen people in Baghdad, including two Reuters news staff, was released on Monday by a group that promotes leaking to fight government and corporate corruption.

The group, WikiLeaks, told a news conference at the National Press Club it acquired encrypted video of the July 12, 2007, attack from military whistleblowers and had been able to view and investigate it after breaking the encryption code.

A U.S. defense official confirmed that the video and audio were authentic.

The helicopter gunsight video, with an audio track of talking between the fliers, shows an aerial view of a group of men moving about a square in a Baghdad neighborhood. The fliers identify some of the men as armed.

WikiLeaks said the men in the square include Reuters photographer Namir Noor-Eldeen, 22, and his assistant and driver Saeed Chmagh, 40, who were killed in the incident.

“The gathering at the corner that is fired up on has about nine people in it,” Julian Assange, a WikiLeaks spokesman said.

The gunsight tracks the two Reuters news staff as the fliers identify their cameras as weapons.

The helicopter initially opens fire on the small group. Minutes later a van comes by, and starts assisting the wounded, and the helicopter opens fire on the van.

David Schlesinger, Reuters’ editor in chief, said of the video released by WikiLeaks that the deaths of Noor-Eldeen and Chmagh were “tragic and emblematic of the extreme dangers that exist in covering war zones.”

“The video released today via WikiLeaks is graphic evidence of the dangers involved in war journalism and the tragedies that can result,” he said.

Reuters has pressed the U.S. military to conduct a full and objective investigation into the killing of the two staff.

Video of the incident from two U.S. Apache helicopters and photographs taken of the scene were shown to Reuters editors in Baghdad on July 25, 2007 in an off-the-record briefing.

U.S. military officers who presented the materials said Reuters had to make a request under the Freedom of Information Act (FOIA) to get copies. This request was made the same day.

Assange said he disagreed with a U.S. military assessment of the incident that the attack was justified.

“I believe that if those killings were lawful under the rules of engagement, then the rules of engagement are wrong, deeply wrong,” he said. The fliers in the video act “like they are playing a computer game and their desire is they want to get high scores” by killing opponents, he said.

WikiLeaks posted the video at www.collateralmurder.com.