Washington - The unprecedented leak of secret United States military reports this week about the war in Afghanistan could have severe consequences for American troops and their allies, and could cost people their lives, Defence Secretary Robert Gates said on Thursday.

In response to the national security breach, the Pentagon has started clamping down on access in the field to sensitive information to reduce the risk of another leak of internal military reports and other sensitive documents, Gates said.

"The battlefield consequences of the release of these documents are potentially severe and dangerous for our troops, our allies, and Afghan partners and may well damage our relationships and reputation in that key part of the world," Gates, a former CIA director, told a news conference.

He said his biggest concern was that Afghans and other allies would no longer trust the United States to keep their secrets safe. "It is amazing how much trust matters," Gates said. "We have considerable repair work to do."

The secret military documents released by the organisation WikiLeaks on Sunday included the identities of some of the Afghans who have given information to US forces.

Mike Mullen, the chairperson of the US military's Joint Chiefs of Staff, said the leakers "might already have on their hands the blood of some young soldier or that of an Afghan family". - Reuters