US President Donald Trump on Saturday again denied that his campaign colluded with Russian operatives, but made no comment on claims that he directly organised hush payments to ward off a possible sex scandal during his White House run.

Trump took to Twitter, his favourite means of communication, to address the multiple court filings that dropped on Friday in connection with special counsel Robert Mueller's sweeping investigation into Russian meddling in the 2016 election.

"AFTER TWO YEARS AND MILLIONS OF PAGES OF DOCUMENTS (and a cost of over $30,000,000), NO COLLUSION!" the president said.

Later, he told reporters: "We are happy with what we are reading. There was no collusion whatsoever. There never has been. The last thing I want is help from Russia on a campaign."

While the filings indeed did not appear to reveal evidence of collusion, they did offer a wealth of new information about what Mueller's team is looking into, along with other federal prosecutors in New York.

Prosecutors directly implicated Trump in efforts to buy the silence of two women who claimed they had affairs with him, saying he directed his then-attorney Michael Cohen to offer them hush money.

"With respect to both payments, Cohen acted with the intent to influence the 2016 presidential election," the New York prosecutors said.

"In particular, and as Cohen himself has now admitted, with respect to both payments, he acted in coordination with and at the direction of Individual-1," they added, referring to Trump.

The payments are technically unrelated to the Russia probe, but prosecutors painted a damning picture of the "extensive, deliberate, and serious criminal conduct" of Cohen -- once a member of Trump's inner circle of trusted aides.

In August, the 52-year-old Cohen pleaded guilty to violating campaign finance law in connection with the payments.

"Cohen deceived the voting public by hiding alleged facts that he believed would have had a substantial effect on the election," prosecutors said.

In a separate sentencing memo, Mueller said that Cohen was in contact with a Russian national as far back as November 2015 who offered "synergy on a government level." That was months before Trump formally won the presidential nomination and well before previously reported contacts.

The Russian national claimed to have ties to the Kremlin and repeatedly proposed a meeting between Trump and Russian President Vladimir Putin.

The individual said the meeting could have a "phenomenal" impact "not only in political but in a business dimension as well," but Cohen never followed up, Mueller said.

That combination of political and business interests could spell trouble for Trump, whose real estate empire was seeking to build a signature tower in Moscow as late as mid-2016 in the midst of his White House bid.

Last week, Cohen pleaded guilty to lying to Congress about the Moscow real estate project. Recent filings in the Mueller probe have suggested the White House knew that Cohen planned to lie to lawmakers about his contacts with Russians. Due to his "relevant" and "substantial" help, Mueller declined to recommend additional jail time, but Cohen is still expected to face four to five years behind bars.

Also on Friday, new twists and turns emerged in the case against Trump's onetime campaign manager Paul Manafort, who was convicted in August of financial fraud and witness tampering charges and pleaded guilty to a second set of charges a month later.

Prosecutors accused Manafort of multiple "lies" to investigators: about his contacts with administration officials even after striking a plea deal; about a debt payment; and about his interaction with a suspected Russian intelligence officer.

The breach of the plea deal could lead to a stiffer jail sentence than the 10 years originally envisaged for the 69-year-old veteran Republican consultant.

Manafort has been convicted mostly on charges related to his work for pro-Moscow politicians in Ukraine between 2004 and 2014. But he has also been investigated for his possible role in alleged campaign collusion with Russia.

Mueller has been inching ever closer to the White House, and on Friday, Trump fired off a volley of tweets against a probe he dubs a "witch hunt," accusing Mueller of "big time conflicts of interest" and alleging he coerced false testimony from witnesses.

For Senate Democrat Richard Blumenthal, a former federal prosecutor, Trump is in legal jeopardy.

"The pieces of the mosaic or the puzzle are coming into place, and the walls are closing in on Donald Trump, and his inner circle, including his family," Blumenthal said.

"I believe he could be indicted and the trial could be postponed until after he finishes service."