Attack video painful to watch, Pentagon chief admits

"It's unfortunate. It's clearly not helpful. But by the same token, I think - think it should not have any lasting consequences," Gates said. The US forces involved were in combat and were operating in split-second situations, he said in Washington on the ABC News television programme This Week.

The Reuters people killed in the 12 July 2007 attack were photographer Namir Noor-Eldeen, 22, and his assistant and driver Saeed Chmagh, 40.

The graphic helicopter gunsight video of the attack has been viewed around the world on the Internet since its release on Monday by WikiLeaks, a website which promotes leaks to fight government and corporate corruption. WikiLeaks said it obtained the encrypted video from military whistleblowers.

Some international law and human rights experts say the Apache helicopter crew  may have acted illegally. Many have been shocked by the images and some of the fliers' comments on the video. Amnesty International called on Wednesday for an independent, thorough and impartial investigation into the incident.

"It's obviously a hard thing to see. It's painful to see, especially when you learn after the fact what was going on. But you – you talked about the fog of war. These people were operating in split-second situations," Gates said.

The US military said an investigation shortly after the incident found that US forces were unaware of the presence of news staff and thought they were engaging armed insurgents, mistaking a camera for a rocket-propelled grenade launcher.

"We've investigated it very thoroughly," Gates said. The military's central command said last week it had no plans to open a new investigation.

David Schlesinger, editor-in-chief, said: "I urge the secretary of defence to meet with me to help ensure a tragedy like this never happens again. We need to have transparency, accountability and an acknowledgment of the vital role journalists play in telling the story of war." ■