Washington, Feb 19 (IANS): US President Donald Trump's former campaign adviser Rick Gates to fraud-related charges within days and has also agreed to testify against Paul Manafort, the lawyer-lobbyist who once managed the campaign, the media reported.

"Rick Gates is going to change his plea to guilty," an informed official told the daily on Sunday.

A revised plea will be presented in a federal court in Washington "within the next few days", the official added.

Gates, a longtime political consultant, can expect "a substantial reduction in his sentence" if he fully cooperates with the investigation, another official told The Los Angeles Times.

Gates is likely to serve about 18 months in prison.

Special Counsel Robert Mueller is heading the prosecutions of Gates and Manafort as part of his wide-ranging investigation into alleged Russian collusion in the 2016 presidential election and whether Trump or his aides committed crimes before, during or since the campaign.

An October 27 indictment showed that prosecutors had amassed substantial documentation to buttress their charges that Manafort and Gates, who were colleagues in political consulting for about a decade, had engaged in a complex series of allegedly illegal transactions rooted in Ukraine.

The indictment alleged that both men, who for years were unregistered agents of the Ukrainian government, hid millions of dollars of Ukraine-based payments from US authorities.

According to the indictment, Gates and Manafort "laundered the money through scores of United States and foreign corporations, partnerships and bank accounts" and took steps to evade related US taxes.

They both had pleaded not guilty.

Once a plea deal is in place, Gates would become yet another known cooperator in Mueller's sprawling probe.