WikiLeaks, which already has made public nearly 500,000 classified US files on the wars in Iraq and Afghanistan, has more US documents for possible release than it has stated, the Pentagon said on Tuesday.

The massive WikiLeaks disclosures of leaked documents have been the largest in US military history, and Pentagon officials are saying that more files may follow.

The whistle-blowing organization has publicly acknowledged it has some 15,000 more documents on the war in Afghanistan that it has threatened to release, along with an Afghanistan video file, the Pentagon noted.

'Those are things they've talked about publicly. And we have reason to believe they have other documents as well,' Colonel Dave Lapan, a Pentagon spokesman, told reporters.

Asked whether the Pentagon had independent knowledge of what WikiLeaks had in its possession, he said: 'We do,' without elaborating.

The US investigation into the source of the leaks has focused on Bradley Manning, a former US Army intelligence analyst in Iraq. Manning is under arrest, charged with leaking a classified video showing a 2007 helicopter attack that killed a dozen people in Iraq, including two Reuters journalists.

No one has yet been charged with leaking any of the more than 70,000 files on the Afghanistan war that WikiLeaks released in July or the nearly 400,000 Iraq war files disclosed last Friday.

Manning's attorney did not return phone calls. The Pentagon has refused to discuss the investigation.

WikiLeaks founder Julian Assange has said the US investigation is also looking into WikiLeaks itself.

Lapan said the Pentagon believes it knows which documents WikiLeaks has in its possession, including a large, encrypted file on its website entitled 'insurance,' which has not been released to the public.

'We believe we know some of what they have,' Lapan said. 'We don't know for certain. For example, we don't know for certain what's in the 'insurance' file. So we don't know exactly everything that WikiLeaks has.'

Earlier on Tuesday in Baghdad, a top Pentagon official said the US Defense Department was considering controls like those that credit card firms use to detect odd behavior to prevent leaks of sensitive information.

'Rather than preventing people from having access to the data, could we do things like credit card companies do, which is to look for anomalous behavior,' Deputy Defense Secretary William Lynn told reporters during a brief visit to Iraq.

'If someone is doing something that doesn't seem appropriate for where they are, downloading 100,000 documents when they are out in some obscure corner of the country, why are they doing that? You go out and ask them,' Lynn said. – Reuters