Former New York City Mayor and attorney to President Donald Trump Rudy Giuliani visits "Mornings With Maria" with anchor Maria Bartiromo at Fox Business Network Studios on September 23, 2019 in New York City.

Former New York City Mayor and attorney to President Donald Trump Rudy Giuliani visits "Mornings With Maria" with anchor Maria Bartiromo at Fox Business Network Studios on September 23, 2019 in New York City. Roy Rochlin—Getty Images

Former New York City Mayor and attorney to President Donald Trump Rudy Giuliani visits "Mornings With Maria" with anchor Maria Bartiromo at Fox Business Network Studios on September 23, 2019 in New York City. - Roy Rochlin—Getty Images

The CEO of Ukraine’s state gas company, Naftogaz, is ready to give evidence in a U.S. federal investigation that is reportedly probing the business dealings of Rudy Giuliani, the CEO said in an exclusive interview on Friday.

“I will with a high likelihood be invited to testify in this case,” Naftogaz CEO Andriy Kobolyev told TIME, citing his lawyers and contacts in the U.S. “If I am called, I would be willing to come and testify,” Kobolyev added.

Federal prosecutors are investigating Giuliani for possible campaign finance violations and illegal lobbying, according to reports published in the past week by Bloomberg and the Wall Street Journal, both of which cited unnamed U.S. officials and sources familiar with the matter.

These reports claimed that the investigation stems from a federal case against two of Giuliani’s associates, Igor Fruman and Lev Parnas, who were indicted last month for allegedly violating campaign finance laws. Giuliani has not been charged with any wrongdoing.

The planned closed-door testimony from Kobolyev, which has not previously been reported, could shed light on recent allegations from U.S. and Ukrainian energy executives that Parnas and Fruman tried to use their connections to Giuliani and the Trump Administration to replace the leadership of Naftogaz, which had resisted their efforts to land a lucrative gas deal in Ukraine.

Asked whether he is preparing to give prosecutors information about Giuliani or about Parnas and Fruman, the executive said, “Both. Everything is connected.”

Giuliani has simultaneously been acting as President Donald Trump’s personal lawyer and diplomatic envoy while pursuing his own lucrative business interests. In one or several of those roles, Giuliani has been working with Fruman and Parnas.

While seeking gas deals in Ukraine this spring, Fruman and Parnas also helped Giuliani to pressure the Ukrainian government to open investigations against President Trump’s political rival, former Vice President Joe Biden. That campaign was later exposed by an intelligence-community whistleblower, whose complaint sparked the ongoing impeachment inquiry against President Trump.

Giuliani, who did not respond to TIME’s request for comment on Friday, has denied allegations of wrongdoing and insisted that he is not involved with a gas company owned by Fruman and Parnas, Global Energy Producers. “I have no personal interest in any business in Ukraine, including that business,” Giuliani told the Journal last week.

Kobolyev declined to comment on what he planned to tell investigators about Giuliani or his two associates: “I would not want to preempt my testimony,” the gas executive told TIME.

A spokesman for the Southern District of New York declined to comment on Friday.

Any testimony from Kobolyev would come on top of the statements that another Naftogaz executive, Andrew Favorov, gave investigators on Thursday in New York City.

Kobolyev interrupted his interview with TIME at his office in Kyiv Friday, saying he wanted to call his colleague Favorov on the phone to ask how his interview with federal investigators had gone, and whether Favorov would be going back on Friday to provide more testimony.

“He finished yesterday,” Kobolyev said after finishing the mid-interview phone call. “He said it was a very unusual experience,” the CEO added, referring to Favorov. “He said he has never gone through questioning like that. I also heard these guys are very, um, very hard, the southern district prosecutors. They’re some of the best in the states.”

Favorov referred questions to a spokesman, who did not respond to a request for comment Friday afternoon.

Citing two unnamed sources familiar with the matter, CNN reported on Nov. 18 that federal prosecutors in New York had contacted people associated with Naftogaz as part of their investigation of Giuliani. Favorov’s U.S. lawyer confirmed to the Associated Press the following day that his client was planning to meet voluntarily with investigators. The timing of that meeting on Thursday, and the fact that prosecutors had not asked Favorov to come back on Friday, have not been previously reported.

The effort by Giuliani’s associates to install new leadership at Naftogaz came to light in an AP report published on Oct. 8. The report described an international effort by Parnas and Fruman to replace the leadership of Naftogaz, which had resisted the attempts of these two businessmen to export American gas to Ukraine under favorable terms.

Parnas and Fruman were arrested at Dulles Airport last month and indicted for allegedly running an unrelated scheme to funnel foreign money to Republican causes and candidates. Both men have pleaded not guilty.

Despite their arrest and the ongoing investigation of Giuliani in New York, the head of Naftogaz says the political campaign to remove him from office may not yet be over. “Some pressure does probably exist,” Kobolyev tells TIME. “But whether it is connected to past events, something that is still inertia from what happened, from attempts that took place in the spring, I can’t say for sure.”

Contact us at letters@time.com.