A US army private under investigation for allegedly leaking classified material to the WikiLeaks website has been transferred from Kuwait to the US amid growing White House and Pentagon anger over this week's revelations about the war in Afghanistan.

Bradley Manning, who has already been charged with leaking a video and other material relating to the Iraq war, is now said to be a suspected source for tens of thousands of documents which made their way via WikiLeaks to the Guardian, the New York Times and Der Spiegel in Germany.

The war logs revealed civilian casualties at the hands of coalition forces that were far larger than previously reported, soaring Taliban attacks and frustration at what allies see as support for the insurgency from within Pakistan. Critics have claimed the leaks put the lives of Afghan informants and coalition troops at risk.

Admiral Mike Mullen, chairman of the US joint chiefs of staff, said yesterday those behind the leaks might already have blood on their hands and the US defence secretary, Robert Gates, promised the criminal investigation would go "wherever it needs to go". He did not rule out the WikiLeaks founder Julian Assange, or the Guardian and other publications being a target.

CNN today reported that Manning, 22, who was an intelligence officer in Iraq, was being held at a Marine Corps facility in Quantico, Virginia. No decision had been made yet as to whether he should face trial for the earlier alleged offences, the news channel said.

Mullen told reporters yesterday: "Mr Assange can say whatever he likes about the greater good he thinks he and his source are doing. But the truth is they might already have on their hands the blood of some young soldier or that of an Afghan family."

Gates said: "We don't know how many more there are out there. It could be a substantial additional number of documents. And we have no idea what their content is, either."

He dismissed the idea of talking to Assange to learn more about further information that might be released. "I'm not sure why we would," he said. "Do you think he is going to tell us the truth?"

Gates did not mention Manning by name as he revealed that the Pentagon was tightening rules for handling classified material in war zones as a result of the leak. Pentagon officials said Manning, who had been stationed at a small post outside Baghdad, may not be the sole target of the army inquiry.

"If the kind of breach involved in the downloading of these thousands of documents had occurred at a rear headquarters or here in the US, there's a very high likelihood we would have detected it," Gates said.

Yesterday the Afghan president, Hamid Karzai, criticised the publication of the war logs, saying that it could endanger Afghans who worked with Nato forces.

"I heard this yesterday … that names of certain Afghans who co-operate with the coalition have been also revealed in these documents. This indeed is extremely irresponsible and shocking," he said. "Because whether those individuals acted legitimately or illegitimately by providing information to Nato forces, they are lives. And the lives are in danger now," he said.

Assange said yesterday that WikiLeaks had contacted the White House via the New York Times and offered to let government officials go through the documents to make sure no innocent people were identified. The White House did not respond to the approach, he told the Australian Broadcasting Corporation.

Assange dismissed allegations that innocent people had been put in danger. "We have yet to see clear evidence of that," he said.