The Pentagon has asked the whistleblower website WikiLeaks to return immediately to the government all versions of classified US military documents obtained by it directly or indirectly from its databases.

"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 spokesperson Geoff Morrell told reporters at a briefing here.

"Public disclosure of additional Defence Department classified information can only make the damage worse. The only acceptable course is for WikiLeaks to take steps immediately to return all versions of all of these documents to the US government and permanently delete them from its website, computers and records," he said.

"WikiLeaks's public disclosure last week of a large number of our documents has already threatened the safety of our troops, our allies and Afghan citizens who are working with us to help bring about peace and stability in that part of the world," Morrell said.

The Department of Defence also demands that WikiLeaks discontinue any solicitation of this type, he asserted.

Morrell, however, denied reports that WikiLeaks has asked the Department of Defence for help in reviewing approximately 15,000 classified documents that it has obtained in an unauthorized and inappropriate manner, before it releases those classified documents to the public.

"WikiLeaks has made no such request directly to the Department of Defence. These documents are the property of the US government and contain classified and sensitive information," he said.

The Pentagon spokesperson clarified that at this point of time it is only a demand to WikiLeaks and is not compelling them.

"If it requires them compelling to do anything -- if doing the right thing is not good enough for them, then we will figure out what other alternatives we have to compel them to do the right thing," he said in response to a question.

Besides the Pentagon, the State Department and the Federal Bureau of Investigation are looking into the various aspects of the leaked classified documents on Afghan War, which official say, has endangered the lives of a large number of US soldiers and Afghan informants.

Morrell said at this point of time, the Pentagon has no idea of what these 15,000 documents contain.

"The fact that information like this gets out into the public domain is a serious breach. We are taking measures internally to reinforce existing rules and guidelines and to make sure that people are aware of those rules and guidelines and are being even more vigilant about enforcing the existing rules and guidelines," he said.

Morrell said WikiLeaks has shown no indication thus far that they appreciate the gravity, the seriousness of the situation they have caused the lives they have endangered, the operations they have potentially undermined, the innocent people who have potentially been put in harm's way as a result.

"This is an opportunity, it seems to me, for them to turn a new page; to recognise the situation that they have created, and to try to rectify it.

If, indeed, these claims that they have made through these third parties -- these spokesmen -- communicated to us through the news media, are serious, if they are serious about engaging with us, they should reach out to us directly. We will consider how to proceed once something like that happens," he said.

Morrell said this is Pentagon's first step to try to compel them, to prevail upon them to do the right thing and return the documents and erase them from their website so that no more additional harm is done, so that this potential database for all of US enemies that now hangs on the Internet and provides an opportunity for them, looking for weaknesses in force protection; tactics, techniques and procedures; all this stuff is potentially out there for people who wish to do the US harm to take advantage of.

"So we're trying to prevail upon them to do the right thing here," he said.