WikiLeaks founder Julian Assange has been charged in the United States, the organization said, in a development that could have implications for Robert Mueller's probe into alleged Russian meddling in the US presidential election.

Prosecutors inadvertently disclosed the existence of a sealed indictment in a court filing in an unrelated case, WikiLeaks said Thursday.

The exact nature of the charges against Assange was not immediately known.

The still-unsealed charges against Assange were revealed by Assistant US Attorney Kellen Dwyer as he made a filing in the unrelated case and urged a judge to keep that filing sealed.

The charges would "need to remain sealed until Assange is arrested," Dwyer wrote according to The Washington Post.

Federal prosecutors have been investigating Assange over WikiLeaks' 2010 publication of a trove of US diplomatic cables that proved an acute embarrassment to Washington.

But the charging of Assange in the US could have implications for special counsel Robert Mueller's probe into whether Donald Trump's election campaign team colluded with Russia to influence the 2016 presidential vote, and whether Trump tried to obstruct the probe into that.

In July, Mueller charged 12 Russian spies with conspiring to hack Democratic National Committee computers, stealing data from the organization and publishing those files in an effort to sway the election.

One of the indictments referred to WikiLeaks, described as "Organization 1," as the platform the Russians used to release the stolen emails.

The 47-year-old Assange has been holed up at Ecuador's embassy in London since 2012, where he took refuge over fears of being extradited to the US over the 2010 WikiLeaks cable dump.