President Donald Trump's personal attorney Rudy Giuliani on Monday denied being involved with a Ukrainian oligarch whose ethical issues have dovetailed with the ongoing impeachment inquiry into the president.

Giuliani also told NBC News he was not planning on visiting Dmitry Firtash, who is currently wanted on corruption charges in the U.S., during a trip to Vienna he planned last week. He said he could not speak for his two Soviet-born business associates, Lev Parnas and Igor Fruman, who were arrested last week on campaign-finance charges in Virginia as they were about to board one-way flights to Vienna. Giuliani has said their similarly timed Austrian trips were not in conjunction.

"I wasn't planning to go see him," Giuliani said. "That was the last thing from my mind on why I was going to Vienna. There was a very important reason I was going that I'm not at liberty to disclose right now that will make it quite clear [Parnas and Fruman] were not fleeing. And I don't know, I can't speak for them, they have their own businesses. I actually do two things with them. I represent their company, and they help me find people. But I'm pretty sure they were going just for the purpose I knew about."

Giuliani insisted he has "nothing to do with Firtash," whose legal team includes Joe diGenova and Victoria Toensing, the pro-Trump husband and wife attorneys who Fox News reported were "working off the books" with Giuliani as part of his Ukrainian venture.

"So, Firtash, I know nothing about," Giuliani said. "I'm not going to answer any questions about because I'm probably going to get it wrong, and you can ask them."

Giuliani also said he has "never" brought up Firtash's extradition battle with Trump.

"I'm not even sure the president is aware of him," Giuliani said. "I think if you asked the president 'who is Dmitry Firtash?' He would say 'I don't know.' As far as I know, we've never discussed him."

One of Ukraine's wealthiest businessman, Firtash has battled extradition charges to the U.S. for the past two years as the Department of Justice seeks to prosecute him over allegations he bribed Indian officials to land a lucrative mining deal. Federal prosecutors labeled him as an "upper-echelon [associate] of Russian organized crime." Firtash has denied that label and the charge, fighting them from Vienna, where he has lived for the past five years.

Parnas has been working for Firtash's legal team as a translator, a spokesman for DiGenova and Toensing told NBC News. The spokesman denied that Parnas' Vienna trip involved Firtash.

As NBC News reported last week, Parnas and Fruman sought to change the leadership at Ukrainian state-run gas company Naftogaz at the same time they were working with Giuliani to uncover information related to former Vice President Joe Biden and his son Hunter's Ukrainian business ties, an effort that is now the subject of the House impeachment inquiry. Naftogaz's existing leadership was hostile toward Firtash's past energy dealings. Giuliani last week denied any involvement with the efforts aimed at Naftogaz.

House Democrats subpoenaed Parnas and Fruman for documents and testimony as part of the impeachment inquiry, which began soon after it was revealed that Trump asked his Ukrainian counterpart in July for "a favor" that included probing the Bidens and investigating a conspiracy involving the 2016 election.

Giuliani has repeatedly highlighted an affidavit former Ukrainian Prosecutor Viktor Shokin filed in behalf of Firtash in which Shokin blamed his ouster on his investigation of Burisma, the Ukrainian gas company affiliated with Hunter Biden. Backed by much of the international community, the former vice president pushed for Shokin's ouster over his ineffectiveness at cracking down on corruption. The probe of Burisma had been dormant for more than a year by the time Shokin was fired and there has never been evidence that either Biden acted inappropriately.

Giuliani told NBC News he had "nothing to do with the preparing of the affidavit" and said he has more evidence to base his claims about Biden on than that document, including an interview with Shokin.

"This is a smear job. The Firtash thing is a smear job. I have nothing to do with him. The president has nothing to do with him," Giuliani said. "The fact is, I know his case because it's very famous. I know the contending positions on both sides of the case, but I have no involvement in it beyond hearing about it and obviously being given an affidavit."

"And all I did was outline the parts of that affidavit that pertain to me," he continued. "I have no idea if the rest of the affidavit is relevant, truthful. I do know the parts of the affidavit that I put out I can support with independent evidence, plenty of independent evidence."