(CNN) Federal prosecutors investigating Rudy Giuliani plan to interview a senior executive of Ukraine's state-run oil-and-gas company, according to his lawyer, as Giuliani's possible ties to a separate natural gas venture have come under scrutiny.

Andrew Favorov, who heads the integrated gas division of the conglomerate Naftogaz, has agreed to speak to prosecutors, his attorney Lanny Breuer said in a statement. Breuer did not share any date, meeting place or other details for the interview.

"The Department of Justice has requested an interview with Andrew Favorov. He has agreed and will voluntarily sit down with the government attorneys," Breuer said. A spokesman for the Manhattan US Attorney's office declined to comment.

Favorov's interview announcement comes after CNN was first to report Monday that prosecutors in the Southern District of New York have contacted people associated with Naftogaz in recent weeks, suggesting investigators have opened an inquiry into whether Giuliani and his associates sought to secure deals by exerting influence over the company.

Giuliani's associates Lev Parnas and Igor Fruman pushed a scheme to replace Naftogaz's chief executive with someone who would favor their own business interests, according to an American energy consultant, Dale Perry, who spoke with Favorov about their efforts.

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