Update: The Associated Press reports, "The Pentagon says it believes the next document dump by WikiLeaks will be even more damaging to national security and the war effort than the organization's initial release of some 76,000 war files."

Pentagon press secretary Geoff Morrell said Thursday that the military believes it has identified the additional 15,000 classified documents that WikiLeaks has vowed to release.

Morrell declined to identify the documents other than to say that their exposure would be ever more damaging than the thousands already published.

LONDON (AFP) – WikiLeaks founder Julian Assange insisted Thursday the whistleblower website still planned to release its final batch of US military files on the Afghan war, despite American demands it hold back.

Speaking via video link to an audience in London, Assange said the site was preparing to release the final 15,000 classified files, the remaining documents from a huge cache which were published last month.

"We are about 7,000 reports in," he said, without giving a date when the files would be released.

Asked whether the website would press ahead with the release, he responded: "Absolutely."

His comments came despite renewed pressure from the Pentagon to withhold the material, and harsh criticism from media freedom group Reporters without Borders, which accused the site of "incredible irresponsibility."

Speaking during a debate at the Frontline Club in the British capital, Assange said that WikiLeaks had received "no assistance, despite repeated requests, from the White House or the Pentagon".

The Pentagon last week demanded WikiLeaks "do the right thing" and return around 70,000 classified US military documents on Afghanistan it released in late July.

It also urged the website to halt plans for any future releases.

In a statement Thursday, Pentagon spokesman Geoff Morrell said the "only responsible course of action for them is to immediately remove all the stolen documents from their website and expunge all classified material from their computers."

Morrell said additional publications would be "the height of irresponsibility" and "would compound a mistake that has already put far too many lives at risk."

The files contained a string of damaging claims, including allegations that Pakistani spies met directly with the Taliban and that deaths of innocent civilians at the hands of international forces were covered up.

But the documents also included the names of some Afghan informants, prompting claims that the leaks have endangered lives.

In an open letter to Assange, Reporters with Borders said it "regrets the incredible irresponsibility you showed when posting your article 'Afghan War Diary 2004 - 2010' on the WikiLeaks website on 25 July."

The group said WikiLeaks had in the past played a useful role by making public information that exposed violations of human rights committed in the name of the US "war against terror."

"But revealing the identity of hundreds of people who collaborated with the coalition in Afghanistan is highly dangerous.

"It would not be hard for the Taliban and other armed groups to use these documents to draw up a list of people for targeting in deadly revenge attacks," it said.

Last week, Morrell said the Defense Department was seeking the return of all versions of documents "obtained directly or indirectly" from Pentagon databases or records.

He said the Pentagon was aware there was other information in WikiLeaks' possession that "has not been pushed into the public domain yet."

"We hope this message will help convince them not to publish," he added.

Assange, 39, an Australian former hacker and computer programmer, has previously said he believed the publication would help focus public debate on the war in Afghanistan and on possible atrocities by US-led forces.

US Defense Secretary Robert Gates and Chairman of the Joint Chiefs of Staff, Admiral Mike Mullen, both said the publication had endangered locals providing information to US-led NATO forces in Afghanistan.

The Pentagon and the Federal Bureau of Investigation swiftly launched an investigation into the case when it came to light July 25.

Daniel Schmitt, a WikiLeaks spokesman in Germany, previously told US news website The Daily Beast that the site wanted to open a line of communication with the Pentagon to review another 15,000 classified reports, in order to "make redactions so they can be safely published."

The Pentagon however has insisted it never received any such request from WikiLeaks.

The site, which styles itself as "the first intelligence agency of the people," was founded in December 2006 and invited would-be whistleblowers from around the world to make anonymous contributions.

WikiLeaks has never identified the source of the Afghan files but suspicion has fallen on Bradley Manning, a US Army intelligence analyst under arrest for allegedly leaking video of a 2007 US Apache helicopter strike in Baghdad in which civilians died.