WASHINGTON/NEW YORK (Reuters) - President Donald Trump’s former national security adviser Michael Flynn has completed his cooperation with the special counsel’s Russia investigation, although he is still aiding another federal probe, according to a court filing on Tuesday.

FILE PHOTO: Former U.S. national security adviser Michael Flynn passes by members of the media as he departs after his sentencing was delayed at U.S. District Court in Washington, U.S., December 18, 2018. REUTERS/Joshua Roberts/File Photo

The disclosure came in a joint court filing between Flynn’s lawyers and Special Counsel Robert Mueller’s office in which they asked for another delay in Flynn’s sentencing, citing his ongoing cooperation with the other federal investigation.

The other investigation is a case brought by prosecutors in the Eastern District of Virginia (EDVA) against Flynn’s former business partner, Bijan Rafiekian, for unregistered lobbying on behalf of Turkey. Rafiekian has pleaded not guilty and Flynn could be a witness at a trial scheduled to begin in July.

“While the defendant remains in a position to cooperate with law enforcement authorities, and could testify in the EDVA case should it proceed to trial, in the government’s view his cooperation is otherwise complete,” Mueller wrote in the filing.

The comment is the latest sign that Mueller may be winding up his 22-month probe into the links between Russia and Trump’s 2016 presidential campaign.

Flynn and Mueller’s office had been given a deadline of March 13 to update U.S. District Judge Emmet Sullivan about Flynn’s cooperation. The deadline was set in December when Sullivan excoriated Flynn, including by suggesting he may have committed treason, and recommended he put off Flynn’s sentencing until his cooperation was complete and he could get full credit for it.

In Tuesday’s filing, Flynn’s lawyers asked to report back again to Sullivan in 90 days.

Flynn has been cooperating with Mueller since pleading guilty in December 2017 to lying to FBI agents about his conversations in late 2016 with Sergei Kislyak, then Russia’s ambassador in Washington, about U.S. sanctions imposed on Moscow by the administration of Trump’s Democratic predecessor, Barack Obama. The conversations took place between Trump’s November 2016 election victory and his inauguration in January 2017.

The indictment against Rafiekian accuses him of working with Turkish government officials on a secret plan to return Muslim cleric Fethullah Gulen, who is living in exile in Pennsylvania, to Turkey -- all without registering as a lobbyist as is required by law.

Flynn worked with Rafiekian, a former director at the U.S. Export-Import Bank, on that project.