Video report by ITV News Washington correspondent Robert Moore

President Donald Trump says a campaign adviser who has admitted to lying to the FBI about meetings with Russian intermediaries was a "low level volunteer" who was "proven to be a liar."

Court documents say George Papadopoulos was approached by people claiming ties to Russia and offering "dirt" on Hillary Clinton in the form of "thousands of emails."

Papadopoulos has pleaded guilty to lying to FBI agents about the conversations.

Trump said the allegations happened "long before" he joined the campaign, but the indictment details allegations stretching from 2006 to 2017.

On Monday Donald Trump's ex-campaign chair Paul Manafort and his business associate Rick Gates were charged with conspiring against the US in the investigation into alleged Russian meddling in the US president's campaign.

Manafort and Gates surrendered to authorities on Monday, before pleading not guilty to all charges in court.

They have been charged with 12 counts, including conspiracy to launder money, failing to register as a foreign agent, false statements, and multiple counts of failing to file reports for foreign bank accounts.

Manafort has been placed under house arrest.

The charges stem from special counsel Robert Mueller's probe into possible ties between Trump's presidential campaign and Russia.

President Trump with Manafort, who was fired as his campaign chairman in August. Credit: AP

Russia says it is not implicated by the first criminal cases against associates of President Donald Trump.

Kremlin spokesman Dmitry Peskov says that "so far Russia doesn't figure in any way in these charges which have been made".

Peskov added that accusations of Russian meddling in the election remain "unfounded," and the Russian government is "observing (the situation) with interest."

The Trump administration has been distancing itself from the three men, with the White House press secretary fielding questions about the charges.

Sarah Huckabee Sanders told reporters the indictment of Paul Manafort "has nothing to do with the president's campaign".

She added that George Papadopoulos was a volunteer member of an advisory council that "literally met one time", and any actions that he took were taken on his own.

There are "indications" Mueller's investigation will be finished soon, she added, refusing to say who gave those indications.

The indictment against Manafort and Gates allege they moved money through hidden bank accounts in Cyprus, St Vincent and the Grenadines and the Seychelles.

In total more than $75 million (£57 million) flowed through the offshore accounts.

Manafort is accused of laundering more than $18 million (£13 million).

In response to the charges the president took to Twitter to dismiss any suggestion of collusion with Russia.

68-year-old Manafort was fired as Trump's campaign chairman in August after word surfaced he had orchestrated a covert lobbying operation on behalf of pro-Russian interests in Ukraine.

President Trump's middle son, Eric Trump, said in an interview at the time that his father was concerned that questions about Manafort's past were taking attention away from the billionaire's presidential bid.

Manafort leaves his home on Monday. Credit: AP

Manafort has been the subject of a longstanding FBI investigation into his dealings in Ukraine and work for the country’s former president, Viktor Yanukovych.

The Associated Press reported he also represented a Russian billionaire a decade ago with the goal of advancing the interests of President Vladimir Putin.

Earlier this year, Manafort's Virginia home was raided by FBI agents searching for tax and international banking records.

He has previously denied any wrongdoing related to his Ukrainian work, saying through a spokesman that it "was totally open and appropriate".

Gates was Manafort's chief deputy and a key player from Trump's campaign.

ITV News Washington Correspondent Robert Moore said if former FBI director Robert Mueller can prove there was collusion between Trump's campaign and the Russians then it is a "significant legal and political challenge" for the president.