US President Donald Trump's former lawyer Michael Cohen said Thursday after testifying in a closed hearing before a congressional panel that he would return on 6 March "to finish up", Reuters reported.

"I am committed to telling the truth and I will be back on March 6 to finish up. There's more to discuss", Cohen was quoted as saying by Reuters after testifying before the House Intelligence Committee on Thursday.

US House Intelligence Committee Chairman Adam Schiff said that Cohen was fully cooperative and answered all panel's questions, adding that the panel would eventually release Cohen's testimony publicly. Schiff also that the US House Intelligence Committee would hear Trump's associate Felix Sater about the Trump's alleged Moscow skyscraper project on 14 March.

READ MORE: Michael Cohen Says He Has No 'Direct Evidence' Donald Trump Colluded With Russia

"I think we all feel it was a very productive interview today where he was able to shed light on a lot of issues that are very important to our investigation. We were able to drill down in great detail", Schiff told reporters after the closed-door testimony.

On Wednesday, Cohen told the US House Oversight Committee that he could not prove what has been so widely alleged for years but remains unverified — that Trump's 2016 campaign colluded with Russia. But the former lawyer suspected that Trump may have known of the leak of private Democratic emails to WikiLeaks and of the meeting between his campaign staff and Russian lawyer Natalia Veselnitskaya.

Cohen has been sentenced to three years in prison for financial crimes that include tax fraud and hush-money payments to two women Trump allegedly had affairs with in violation of campaign finance laws. He also pleaded lying to Congress.

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The US president’s former lawyer remains out of prison to continue cooperating with special counsel Robert Mueller's probe into the alleged Trump-Moscow collusion during the 2016 US presidential election. Moscow and the Trump team have denied the allegations since they were raised.