Special Counsel Robert Mueller's office has said US President Donald Trump's ex-national security adviser Michael Flynn provided "substantial" cooperation with its probe into possible collusion between Trump's campaign team and Moscow.
In a court filing, Mueller's office said Flynn assisted with the investigation "concerning links or coordination between the Russian government and individuals associated with the Trump campaign."
Flynn also provided "firsthand information about the content and context of interactions between the transition team and Russian government officials," the filing said.
Mueller's office, citing 19 interviews provided by Flynn to Mueller's office and other federal prosecutors, asked a federal judge not to sentence him to prison.
Flynn also provided help on other criminal investigations, although those details were redacted from the filing because the probes are ongoing.
Flynn, who held the White House job for only 24 days, pleaded guilty in December 2017 to lying to the FBI about his contacts with Russia.
He will be sentenced in the US District Court for the District of Columbia on December 18.
He is so far the only member of Trump's administration to plead guilty to a crime uncovered during Mueller's wide-ranging investigation into Russian attempts to influence the 2016 US election and potential collusion by Trump aides.
Mueller's probe, which could threaten Trump's presidency, has already ensnared 32 individuals and three Russian firms. He is expected to issue a report on his findings possibly next year.
In addition to Flynn, others who have since been charged by Mueller include Trump's former campaign manager Paul Manafort and campaign deputy Rick Gates, as well as Trump's former personal lawyer Michael Cohen, who pleaded guilty last week to lying to Congress about a proposed Trump Organisation skyscraper in Moscow.
Trump has called Mueller's probe a witch hunt and has denied colluding with Russia. Moscow denies trying to interfere in the elections.
Flynn, a retired army general, was forced to resign in February 2017 as national security adviser after he was found to have misled Vice President Mike Pence about discussions he had with Russia's then-ambassador Sergei Kislyak.
Under a plea bargain deal, Flynn admitted in a Washington court that he lied when asked by FBI investigators about conversations with Kislyak just weeks before Trump took office.
Prosecutors said the two men discussed US sanctions against Russia and that Flynn also asked Kislyak to help delay a UN vote seen as damaging to Israel.
Flynn's crime of lying to the FBI carries a statutory maximum sentence of five years in prison. His plea agreement states, however, that he is eligible for a sentence of zero to six months and can ask the court not to impose a fine.
