Rudy Giuliani has sought to discredit the federal investigation into his dealings in Ukraine a day after agents raided his home and office.
On his daily talk show on WABC Radio, Giuliani referred to prosecutors in the US Attorney's Office for the Southern District of New York, which he used to run, as unaccomplished "bullies".
"You're not going to stop me. And you're not going to convict me of some phoney crime," Giuliani said.
He then ticked off a list of his own accomplishments as the US attorney in Manhattan in the 1980s, including prosecutions of mob figures and Wall Street fraudsters.
"And what have they done? What have they done? Nothing, except come after me ... at six o'clock in the morning with a piece of nonsense. No wonder they're jealous," Giuliani said.
The federal probe is examining Giuliani's ties to Ukraine and whether he violated a federal law that governs lobbying on behalf of foreign countries or entities.
Giuliani, the Republican former mayor of New York City, has insisted that all of his activities in Ukraine were conducted on behalf of former president Donald Trump.
At the time, Giuliani was leading a campaign to press Ukraine for an investigation into President Joe Biden and his son Hunter.
But some Ukrainian figures who were in contact with Giuliani have said in interviews that they also hoped he could help them on matters in the US, including arranging for meetings with the US attorney-general and ousting the US ambassador to Ukraine, Marie Yovanovitch.
The search warrants for Giuliani's electronic devices were approved by a federal judge.
On his radio program, Giuliani said he wouldn't talk in detail about the case, but he again denied doing work on behalf of any foreign entities.
He previously told The Associated Press he had "never represented a foreign anything before the US government".
The US attorney's office in Manhattan declined to comment.
In the decades since Giuliani left, the office has handled some of the nation's most high-profile prosecutions, convicting global drug traffickers, corrupt politicians, Wall Street fraudsters and terrorists including the men behind the 1993 bombing of the World Trade Center.
White House press secretary Jen Psaki said Thursday on CNN that the White House was given no heads' up on the fact the raid was coming.
The Justice Department, she said, "is independent now. They're going to make their own decisions, take their own actions. That's how the president wants it."
Trump told Fox Business on Thursday that Giuliani was "the greatest mayor in the history of New York" and "a great patriot".
"It's very, very unfair," he said of what happened on Wednesday.
"Rudy loves this country so much, it is so terrible when you see things that are going on in our country with the corruption and the problems and then they go after Rudy Giuliani."
