"These documents are the property of the U.S. government and contain classified and sensitive information," Pentagon spokesman Geoff Morrell said in a press conference Thursday, the video of which is available online.
He demanded that "all versions" of them be returned to the U.S. government immediately.
Morrell also refuted published reports that Wikileaks asked the Department of Defense for help in reviewing the files before releasing them to the public. "Wikileaks has made no such request directly to the Department of Defense," he said.
Later, though, another post from the site seemed to take the request a bit more seriously. "We are examining the Pentagon's 'request' and will issue a statement in due course," Wikileaks said. So far, however, no formal statement has been issued.
Wikileaks also refuted Morrell's claim that the DoD received no document-review request from the site. "Don't be fooled by Pentagon rhetorical tricks," according to a Twitter post, which said the site requested help through an "agreed intermediary."
Wikileaks has consistently run afoul of authorities and governments worldwide for obtaining often classified documents and publishing them online. Proponents of the site, however, praise it for bolstering freedom of speech and representing an important tool for journalists.
The heat from the U.S. government on Wikileaks intensified two months ago when the DoD arrested a military intelligence analyst for allegedly leaking the video of a 2007 U.S. helicopter attack on people assembled in a Baghdad square. The attack left two Reuters employees dead and two children wounded.
The latest skirmish started on July 25 when Wikileaks released a batch of more than 75,000 files called the Afghan War Diary 2004-2010, regarding the current conflict in Afghanistan. The files depict a war in which an alarming number of civilians have been killed and caused an outcry of criticism from the press and public about U.S. military failures in the region.
The 15,000 documents currently at issue would have been released at the same time but their disclosure was delayed so Wikileaks could remove names and other sensitive information.