Pentagon to ask for FBI assistance in search for 'whistleblower' on Afghanistan

US Defence Secretary Robert Gates has called in the FBI to ensure the search for the whistleblower(s) "can go wherever it needs to go".

The Army is leading the inquiry inside the Defence Department into who passed 91,000 secret military documents to WikiLeaks.

They are looking most closely at Pvt. Bradley Manning, an Army intelligence specialist who has already been charged with leaking other material to the website.

Gates said the FBI would concentrate on persons outside of the department and would not rule out the founder of WikiLeaks, Julian Assange, as a possible target.

Both he and chairman of the Joint Chiefs of Staff, Mike Mullen, accused the website's release of threatening the lives of Afghans who have helped the coalition war effort.

"Assange can say whatever he likes about the greater good he thinks he and his source are doing," Mullen said.

"But the truth is they might already have on their hands the blood of some young soldier or that of an Afghan family."

Assange said he had "yet to see clear evidence" to reinforce the claim, in an interview with the Australian state broadcaster the ABC.

He said the White House had denied an opportunity to examine the documents before the release to ensure no innocent people were identified.

The officials had not responded to the approach, which had been made via the New York Times, he said.

Gates confirmed the Pentagon is tightening rules for handling classified material in war zones as a result of the unprecedented leak.