US President Donald Trump's longtime political ally Roger Stone has pleaded not guilty to charges he tried to obstruct a congressional investigation into allegations Russia meddled in the 2016 presidential election.

Key points: Indictment alleges Mr Stone had advanced knowledge of WikiLeaks' release of emails that damaged the Clinton campaign

Indictment alleges Mr Stone had advanced knowledge of WikiLeaks' release of emails that damaged the Clinton campaign Mr Stone smiled when arriving at court, and was swarmed by protesters and supporters

Mr Stone smiled when arriving at court, and was swarmed by protesters and supporters He has been a key Republican operative since the days of the Richard Nixon Watergate scandal

The self-proclaimed 'dirty trickster', who arrested on Friday in an early-morning raid on his home in Florida, became the latest member of Mr Trump's inner circle charged in Special Counsel Robert Mueller's Russia investigation.

On arriving at the US Federal Court in Washington wearing a blue suit and tie, Mr Stone smiled as he passed through a gauntlet of reporters.

A small group of protesters waved Russian flags and a placard that said "Dirty Traitor" while other people showed their support for the 66-year-old veteran Republican operative, chanting: "Free Roger Stone."

His lawyer Robert Buschel said Mr Stone pleaded not guilty to the charges of making false statements to Congress, obstruction of an official proceeding and witness tampering.

The indictment said Mr Stone told members of Mr Trump's 2016 presidential campaign that he had advance knowledge of plans by the WikiLeaks website to release damaging emails about Mr Trump's Democratic opponent, Hillary Clinton, that US intelligence agencies have concluded were stolen by Russia.

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The indictment did not indicate whether Mr Stone knew Russians had stolen the emails by hacking into computers used by Mrs Clinton's senior campaign adviser, John Podesta, and the Democratic National Committee.

Mr Mueller last year charged 12 Russians accused in the hacking as part of his investigation of Russia's role in the 2016 election, whether Mr Trump's campaign conspired with Moscow and whether the President unlawfully sought to obstruct the investigation.

The charges against Mr Stone marked the first time Mr Mueller's team has publicly tied the Trump campaign to WikiLeaks, and raised questions about what Mr Trump might have known prior to the public release of the stolen emails.

The charging documents said a senior campaign official, "was directed to contact Mr Stone about any additional releases and what other damaging information" WikiLeaks had about Mrs Clinton's campaign but do not disclose the identity of the person who gave the order.

Mr Stone, a Republican political operative since the days of the Watergate scandal that forced his former boss, president Richard Nixon, to resign in 1974, was released on a $US250,000 bond after his arrest.

He has declared his innocence and, in comments to journalists on Monday in Florida ahead of his arraignment, accused Mr Mueller of "a raw abuse of power".

Thirty-four people have been swept up in the Mueller investigation. Those charged include Mr Trump's former campaign chairman and deputy campaign chairman, former national security adviser and his former personal lawyer.

It remains unclear whether any further charges have been filed.

Acting US Attorney-General Matthew Whitaker on Monday said Mr Mueller's investigation was close to wrapping up and that a report was expected soon.

Reuters