Former Trump campaign manager Paul Manafort held secret meetings with WikiLeaks founder Julian Assange inside the Ecuadorian embassy in London, the Guardian reported Tuesday, citing unnamed sources.

The British publication said Manafort went to see Assange in 2013, 2015 and then around the time he joined the campaign.

The Guardian said, according to a "well-placed source," a casually dressed Manafort met with Assange for about 40 minutes around March 2016. Ecuadorian sources said the visit would normally have been logged, but they told the Guardian the 2016 visit was not. The paper said it was "unclear why Manafort wanted to see Assange and what was discussed."

Manafort, 69, told the newspaper the story is "100 percent false."

In a separate statement, Manafort, now in jail awaiting sentencing on two financial fraud convictions, went on to characterize the article as "deliberately libelous."

"I have never met Julian Assange or anyone connected to him," Manafort said in a statement distributed by his spokesman. "I have never been contacted by anyone connected to Wikileaks, either directly or indirectly. I have never reached out to Assange or Wikileaks on any matter."

"We are considering all legal options against the Guardian who proceeded with this story even after being notified by my representatives that it was false,” he said.

Special counsel Robert Mueller has made contacts between Assange and people connected to President Donald Trump's 2016 campaign a focus of his investigation into Russian election meddling. WikiLeaks published emails damaging to the Democratic National Committee and Trump's opponent Hillary Clinton ahead of the election – emails that U.S. intelligence agencies concluded were stolen by Russian intelligence officers.

Mueller has searched for evidence that people in Trump's orbit had advance knowledge of the emails as part of his inquiry into potential collusion between the Trump campaign and the Kremlin's efforts to sway the election.

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Manafort's reported contact with Assange could shed new light on Mueller's efforts to tie the campaign to Assange, which so far have focused on former Trump adviser Roger Stone and conservative conspiracy theorist Jerome Corsi.

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Manafort is currently awaiting sentencing after being convicted in August on eight counts of financial fraud in a federal court in Alexandria, Virginia. He also entered a separate guilty plea in the District of Columbia as part of deal with the government in which he agreed to cooperate with Mueller's team.

But on Monday, the special counsel's office said Manafort lied repeatedly to the FBI after agreeing to cooperate and recommended that he get no credit to reduce his prison sentence. He faces the prospect of perhaps a decade in prison in the D.C. case alone.

Assange has taken refuge in Ecuador's embassy in London since 2010, largely out of concern the U.S. would seek his extradition on charges related to WikiLeaks' publication of confidential State Department cables.

Last week, prosecutors inadvertently disclosed that "Assange has been charged" in an unrelated case, although it was not revealed what the charges were, nor when and where the alleged crime occurred. A judge is currently reviewing journalists' request to unseal the charges.

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"If true, the revelation that Paul Manafort repeatedly met with Julian Assange in the Ecuadorian Embassy in London raises serious new questions about Mr. Manafort’s relationship with WikiLeaks," Sen. Bob Menendez, D-N.J., said in a statement Tuesday.

"Given that Secretary Pompeo met with Ecuadorian Foreign Minister Valencia yesterday morning, the State Department and the intelligence community must immediately brief the Senate Foreign Relations Committee on Mr. Manafort’s interaction with Mr. Assange, as well as the Ecuadoran governments role in any meetings," Menedez said. "Similarly, as evidence continues to mount about WikiLeaks interference in the 2016 U.S. election, Ecuador’s government must reevaluate the risks of harboring an individual who has damaged democratic processes around the world."

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Contributing: Kevin Johnson