Donald Trump has said there was "absolutely no collusion" between his presidential campaign and Moscow after a former adviser admitted lying to the FBI about contacts with Russia.

Mr Trump was speaking to reporters as he left the White House a day after his former national security adviser, Michael Flynn, pledged to cooperate with special prosecutor Robert Mueller's probe into Russia's meddling into the election.

Mr Trump told reporters: "What has been shown is no collusion, no collusion. There's been absolutely no collusion."

Mr Flynn also pleaded guilty to lying to the FBI about contacts he had with the Russian ambassador.

A number of US media outlets have claimed that Mr Trump's son-in-law and senior aide Jared Kushner was the "very senior" member of the President's transition team who directed Flynn to reach out to Russia.

According to reports, this was in an attempt to delay or defeat a UN resolution on Israeli settlements before Mr Trump took office.

The allegation comes as Mr Flynn pleaded guilty to lying to the FBI over his conversations last December with the Russian ambassador to the US, Sergey Kislyak.

As part of the plea agreement, retired three-star general Mr Flynn has agreed to co-operate with an investigation led by special counsel Robert Mueller.

Mr Mueller and a team of prosecutors are looking into accusations of Russian meddling in the presidential election and potential collusion by Mr Trump's campaign.

Court papers suggested senior Trump transition officials were fully aware of Mr Flynn contacting Russian officials in the weeks before January's inauguration.

The court documents set out the directions given to Mr Flynn by a Trump transition official about how to interact with Russia regarding sanctions the Obama administration imposed for alleged Russian meddling in the election.

Mr Flynn and the official reportedly spoke about "the potential impact of those sanctions on the incoming administration's foreign policy goals" and that Mr Flynn then called Mr Kislyak, and "requested that Russia not escalate the situation".

The White House has rejected the idea that Mr Flynn could implicate "anyone" else but himself.

Guilty plea

President Donald Trump's former national security adviser Michael Flynn pleaded guilty on Friday to lying to FBI agents about his contacts with Russia's ambassador, and agreed to cooperate with prosecutors. Credit: Jack Gruber-USA TODAY/Sipa USA

After a federal court appearance in Washington on Friday, Mr Flynn said: "I recognise that the actions I acknowledged in court today were wrong.

"My guilty plea and agreement to cooperate with the special counsel's office reflect a decision I made in the best interests of my family and of our country. I accept full responsibility for my actions."

The charge normally carries up to five years in prison but under the terms of a plea deal, Mr Flynn faces a lighter sentence of only up to six months in jail, court filings show.

White House lawyer Ty Cobb said: "Nothing about the guilty plea or the charge implicates anyone other than Mr Flynn."

Mr Cobb described Mr Flynn as "a former Obama administration official" who was only at the White House for "25 days".

The charges related to events late last year, during the transition period between President Obama and President Trump, when the US imposed sanctions on Russia, and when a United Nations Security Council resolution was pending.

Mr Flynn was interviewed by the FBI just days after Mr Trump's inauguration on 20 January, before being forced to resign in February after White House officials claimed he had misled them about whether he had held discussions with Mr Kislyak.

Another former senior aide to Mr Trump, Paul Manafort, who ran his campaign for president for several months last year, was charged in October with conspiring to launder money, conspiracy against the United States and failing to register as a foreign agent of Ukraine's former pro-Russian government.

Mr Manafort, who did not serve in Mr Trump's administration, and a business associate who was charged with him, pleaded not guilty.

Mr Flynn is the first person who actually worked in the White House to be charged.

Mr Kushner, who is married to the President's eldest daughter Ivanka, has denied any wrongdoing.

Mr Trump is said to have taken a particular interest in the Flynn investigation. Former FBI Director James Comey has claimed that during a private meeting in the Oval Office, Mr Trump asked him to consider ending the investigation into Mr Flynn.

Mr Comey said he was so unnerved by the meeting that he prepared an internal memo about it. The assertion has been denied by the White House.

The dismissal of Mr Comey by the President in May precipitated the appointment of Mr Mueller as special counsel.