US Defence Department demanded that whistle-blowing website WikiLeaks return all US secret documents on the war in Afghanistan and erase the classified data already posted on the Internet.
Last month, WikiLeaks released some 71,000 US military secret files on the war in Afghanistan dating from September 2004 to December 2009. The website is believed to have at least 15,000 more files with classified data.
"The Defence Department demands that WikiLeaks return immediately to the US government all versions of documents obtained directly or indirectly from the Department of Defence databases or records," Pentagon spokesman Geoff Morrell said on Thursday.
"We are asking them (WikiLeaks) to do the right thing. This is the appropriate course of action given the damage that has been done," Morrell said.
The leaked documents contain a massive amount of classified data, from reports on the killings of civilians and lists of names of Afghan informers helping NATO troops, to reports that Pakistan's ISI intelligence agency is helping the Taliban in Afghanistan.
US Defence Secretary Robert Gates earlier said the publication of Afghan war files may lead to serious consequences for NATO troops and their Afghan assets.
Afghan President Hamid Karzai has denounced leaking the names of Afghan informants, saying "their lives will be in danger now".
The Pentagon, the FBI and the Justice Department are jointly probing the leaks.
The main suspect in the leak of the documents is jailed US private Bradley Manning, who had top-secret clearance as an intelligence analyst for the army when he was stationed in Iraq.
Pentagon investigators believe that Manning has accessed a worldwide military classified internet and e-mail system to download the documents.
Manning, 22, was charged in June with several violations of the US Criminal Code for allegedly transferring classified data without authorization.
Earlier this year, the Wikileaks website posted a video showing US troops firing repeatedly on a group of men, some of whom were unarmed, walking down a Baghdad street.
The website does not have a central office or any paid staff and its operations are run only by a small dedicated team and some 800 volunteers.
Wikileaks' founder, Australian activist Julian Assange, has no home address but he often pops up in Sweden and Iceland, where internet anonymity is protected by laws. He is being hunted by Pentagon investigators and as is suspected of releasing confidential US State Department documents.