Washington, May 28 (IANS): Donald Trump's lawyer Rudy Giuliani has defended the US President's political attacks against special counsel Robert Mueller's investigation into possible Russian collusion, suggesting that the origins of the probe were illegitimate, the media reported.

Asked during a CNN interview on Sunday whether there was a larger strategy to undermine the investigation at play, Giuliani said he "couldn't do it if they didn't have the material".

"They're giving us the material to do it. Of course, we have to do it in defending the President. To a large extent, what we're doing here, it is the public opinion, because eventually the decision here is going to be impeach or not impeach," Giuliani said.

The lawyer also suggested that the start of the Mueller probe was illegitimate, citing fired FBI Director James Comey's leaked memos and a lack of evidence of collusion between Trump and Russia.

"You get the Comey thing, which is the leak of a confidential memo, which is illegal for an FBI official to do. I'm not saying Mueller is illegitimate. I'm saying the basis on which he was appointed was illegitimate," Giuliani remarked.

Asked whether the Mueller probe was legitimate now, Giuliani told CNN "not anymore", citing reports of an FBI informant within the Trump campaign as one of the reasons for its discrediting.

The former New York City mayor also said the President was "adamant" about doing a sit-down interview with Mueller.

Giuliani said two topics were likely to be addressed during the interview: collusion and obstruction of justice.

Mueller has been pursuing his investigation since May 2017 to determine if - as US intelligence agencies say - the Kremlin interfered with the 2016 presidential vote to favour Trump and whether or not members of Trump's campaign colluded with that effort.