Washington: Former top FBI official Andrew McCabe said he began an obstruction of justice and counterintelligence investigation into US President Donald Trump and his ties to Russia after Trump fired bureau director James Comey in May 2017, CBS News reported on Thursday.

McCabe, who became acting director after Comey's firing, said he was disturbed by his conversation with Trump following Comedy's dismissal and got the investigations started the following day, according to excerpts from an interview with 60 Minutes to be broadcast on Sunday.

"I was speaking to the man who had just run for the presidency and won the election for the presidency and who might have done so with the aid of the government of Russia, our most formidable adversary on the world stage. And that was something that troubled me greatly," McCabe said in his first TV interview.

In the first public confirmation of the investigation by an official who was involved, McCabe described events that occurred in the eight days between Comey's firing and the appointment of special counsel Robert Mueller to take over the investigations of Russian interference in the 2016 US election, CBS said.