Two former Donald Trump associates were indicted Monday and it was revealed another has pleaded guilty to lying to FBI investigators, in the first substantial legal action stemming from the probe into Russia's US election interference.

There is nothing to date that directly ties the president to Russian efforts to sway the 2016 election. But actions by his aides, and his refusal to strongly condemn Moscow interference, have fueled lingering suspicions.

Here is an outline of what we know about the indictments and charges.

- Who's been charged? -

Trump campaign chairman Paul Manafort is the highest-profile figure in the president's orbit to face charges in the probe led by special counsel Robert Mueller.

The White House has said Manafort, who began working for the campaign in March 2016 and resigned under pressure five months later, "played a very limited role for a very limited amount of time."

Manafort, 68, pleaded not guilty Monday afternoon hours after he and business partner Rick Gates turned themselves in to the FBI.

Gates, 45, is a Manafort business partner who served as Manafort's deputy during the campaign. While Manafort was forced out, Gates reportedly stayed on, with a role in the presidential transition team.

George Papadopoulos -- who pleaded guilty on October 5 to making false statements, according to court documents unsealed Monday -- was a foreign policy advisor on Trump's campaign. In 2016 he met with Russia contacts and sought meetings between Trump campaign officials and members of Russian President Vladimir Putin's office.

The guilty plea by Papadopoulos, who was arrested July 27, is seen as the sharpest evidence yet of possible collusion between the campaign and Russia.

- What are the charges? -

A 31-page indictment details 12 charges against Manafort and Gates, including conspiracy against the United States and conspiracy to launder money.

The two stand accused of hiding millions of dollars earned working for former Ukrainian politician Viktor Yanukovych and his pro-Moscow political party, and avoiding paying taxes on the income.

Manafort and Gates were also charged with not filing reports of foreign bank accounts, and not registering as agents of a foreign power as they lobbied the US government on behalf of Ukraine.

Papadopoulos pleaded guilty to making false statements, and hiding contacts with a Moscow-linked professor offering "dirt" on Trump's election rival Hillary Clinton.

- Trump's reaction -

The president has long dismissed the Russia investigation as "fake news." He reacted dismissively to Monday's announcements, even seeking to turn attention to Clinton.

"Sorry, but this is years ago, before Paul Manafort was part of the Trump campaign. But why aren't Crooked Hillary & the Dems the focus?????" he posted on Twitter.

"Also, there is NO COLLUSION!"

Several Democratic lawmakers warned Trump Monday not to interfere with Mueller's probe. The White House said he had no plans to change the special counsel.

- Explosive highlights -

Papadopoulos confessed he had lied to FBI investigators about his extensive meetings with Russian contacts and his efforts to, in the words of the court document, "arrange a meeting between the Campaign and Russian government officials."

He emailed Trump campaign contacts saying he had met with a female Russian national whom he described as "Putin's niece," in an effort to coordinate a meeting between the campaign and "Russian leadership."

Papadopoulos admitted that in April 2016 he met with a professor claiming close contacts to Russian officials who had obtained "dirt" on Clinton, as well as "thousands" of her emails.

The Manafort indictment details brazen illegal activity. The pair moved more than $75 million through offshore accounts and shell companies between 2006 and 2016.

They laundered $18 million. The tax-free money helped Manafort fund a "lavish lifestyle" that included purchasing multi-million-dollar properties and luxury goods and services for himself and family.

Source: AFP