Washington, Feb 16 (IANS): US President Donald Trump's former campaign adviser Rick Gates was finalising a plea deal with special counsel Robert Mueller, indicating that he would cooperate in the ongoing Russian collusion probe, the media reported.

Gates has already spoken to Mueller's team about his case and has been in plea negotiations for about a month, informed officials told CNN on Thursday.

He has had what criminal lawyers call a "Queen for a Day" interview, in which a defendant answers any questions from the prosecutors' team, including about his own case and other potential criminal activity he witnessed.

Meanwhile, Mueller's investigators were planning to file new charges against Gates that are tax-related, sources familiar with the investigation told CNN.

The additional charges could be used to pressure Gates into cooperating with Mueller's team.

Additional charges against former Trump campaign chairman Paul Manafort are also being prepared. Gates's plea deal could be announced within the next week.

Gates hired a top white-collar attorney last month that was spotted meeting twice with Mueller's team.

The former business associate of Manafort pleaded not guilty in October 2017 to eight charges in the probe, including money laundering. Manafort also pleaded not guilty to charges in the same case.

However, it was still unclear what Gates, who outlasted Manafort in the campaign and later worked on the Trump inaugural efforts, could share that would be of value to the Russian collusion investigators.

Mueller has filed charges against four figures tied to President Trump in his probe, including Gates and Manafort, reports The Hill magazine.

Former National Security Adviser Michael Flynn and former Trump campaign adviser George Papadopoulos have both pleaded guilty to charges from Mueller.

Flynn and Papadopoulos have agreed to cooperate with Mueller in the investigation.