Donald Trump's personal lawyer on Sunday called for an investigation into special counsel Robert Mueller's Russia probe, claiming it was tainted from the outset under former FBI director James Comey.

"We want the Mueller probe to be investigated the way the Trump administration has been investigated," Rudy Giuliani said on CNN's "State of the Union."

Giuliani's comments were the latest in a barrage of attacks on the probe by the president and his lawyers as Mueller appears to be nearing a conclusion to his investigation into possible collusion between Trump's campaign and Moscow.

"WITCH HUNT! There was no Russian Collusion. Oh, I see, there was no Russian Collusion, so now they look for obstruction on the no Russian Collusion. The phony Russian Collusion was a made up Hoax," Trump tweeted on Sunday.

"Too bad they didn't look at Crooked Hillary like this. Double Standard!" he added, referring to his 2016 Democratic presidential rival Hillary Clinton.

The Washington Post reported Sunday that Mueller is pressing to wrap up his findings by the end of summer and, in the words of former Republican leader Newt Gingrich, Trump and his allies were "prepared for war."

"We want to see if we can have the investigation and special counsel declared illegal and unauthorized," Giuliani, a former New York mayor and federal prosecutor, told the Post in an interview Friday.

Mueller has been investigating possible obstruction of justice as well as contacts between Trump campaign officials and a Russian effort to sway the 2016 presidential race in Trump's favor.

So far, 20 people have been indicted and at least four are cooperating with Mueller's investigators.

The Post reported Sunday that Roger Stone, a onetime Trump advisor, has acknowledged meeting a Russian national who was offering dirt on Clinton in May 2016, but said the man wanted money and nothing came of it.

In his appearance on CNN, Giuliani argued that the Mueller probe was tainted from the start, thanks to Comey.

"I believe that the Mueller investigation should be investigated not because necessarily of Mueller but because of its genesis in this very, very now completely almost illegal and unethical probe, this Russian probe," he said.

"I'm saying what led up to the special counsel. I don't think Mueller and his people need to be investigated, unless something comes out of that," he said.

Trump fired Comey in May last year, later admitting that the Russia probe was on his mind when he did so, which in turn ramped up suspicions of obstruction of justice.

Giuliani argued, however, that the Mueller probe was based on Comey's contemporaneous notes of his private meetings with Trump before his firing, which the lawyer claimed was "illegally leaked."

"That usually leads the court to say the thing is tainted. They may come out with a lot of problems if they don't get this resolved," he said.

Giuliani also pointed to a Justice Department inspector general's report as vindication of the president's position.

That report criticized Comey's decision-making investigation involving a probe into Clinton's use of a private email server.

But while it found instances in which FBI investigators expressed bias against Trump in private emails, it concluded there was no evidence that the sentiments played into the investigation itself.

In a subsequent interview on Sunday with CBS's "Face The Nation" show, Giuliani said the Mueller probe should face both an international government investigation by the Justice Department's inspector general and a grand jury probe.

"It's crying out for someone to investigate the investigators. There should be a full and complete [inspector general] report and grand jury investigation of what happened here, after it became the Russia probe," Giuliani said. "What was the purpose of it? What did they gather?"

Giuliani said that "troubling unethical behavior" among some Justice Department (DOJ) officials had tainted Muller’s probe.