WASHINGTON (BLOOMBERG) - US President Donald Trump resumed his verbal assault on the special counsel investigation probing Russian interference in the 2016 presidential election with a fresh series of Twitter messages on Saturday (May 26).

"This whole Russia Probe is Rigged," Mr Trump said in one of three tweets that appeared as his motorcade returned to Washington from his golf course in suburban Virginia, where he spent about four hours.

"#SPYGATE & CONFLICTS OF INTEREST!"

The President repeated an unsubstantiated claim that an FBI informant who contacted advisers to his campaign was a political "spy", days after Justice Department officials briefed lawmakers on classified materials about the probe into Russian meddling in the election.

"With Spies, or 'Informants' as the Democrats like to call them because it sounds less sinister (but it's not), all over my campaign, even from a very early date, why didn't the crooked highest levels of the FBI or 'Justice' contact me to tell me of the phoney Russia problem?" Mr Trump said.

The Justice Department held two meetings on Thursday with lawmakers - at Mr Trump's demand - after revelations that the FBI had a confidential informant who had long helped the bureau make contact with three advisers to his campaign.

While the President has continued to tweet denunciations of what he's calling "SPYGATE", there's no evidence the informant worked inside his campaign.

House Speaker Paul Ryan said after the meetings that Republicans are now "getting the cooperation necessary" to resolve their demands for the classified information.

Representative Adam Schiff, the top Democrat on the House Intelligence Committee, told reporters there's "no evidence to support any allegation the FBI or any intelligence agency planted a spy in the Trump campaign".