Donald Trump launched an angry denunciation of the official probe into his election campaign’s alleged ties to Russia yesterday as it emerged the federal investigation could make its first arrest as early as Monday.

Senior Republicans also stepped up attacks on Robert Mueller, the man leading the investigation into alleged Russian attempts to sway last year’s American election, criticising leaks and demanding he step aside.

US media reported that the first arrests from Mr Mueller’s investigation - possibly including some of Mr Trump’s senior former advisers - could come on Monday after a grand jury approved its first Russia-related indictment on Friday.

The revelation sparked a weekend of feverish speculation about who would be indicted as well as frantic Republican efforts to discredit the investigation.

In a furious and defensive barrage of tweets on Sunday morning, Mr Trump dismissed the allegations as “phony” and the investigation as a “witch hunt”, complaining that allegations against Hillary Clinton had not been examined in the same detail.