(CNN) Federal prosecutors in New York who are investigating Rudy Giuliani are seeking to interview people with knowledge of Ukraine's state-run oil-and-gas company, Naftogaz, according to two people familiar with the matter, suggesting investigators have opened a line of inquiry into whether Giuliani and his associates sought to secure energy deals by asserting influence on the company.

Prosecutors in the Southern District of New York have contacted people associated with the company in recent weeks, said the sources, who asked not to be identified because of the sensitivity of the matter. A spokesman for SDNY declined to comment. There is no indication of wrongdoing by Naftogaz.

Naftogaz stands at the center of an effort by Giuliani associates Lev Parnas and Igor Fruman, and their purported natural-gas company, Global Energy Producers, to replace Naftogaz's chief executive officer with someone who would be more beneficial to their own business interests earlier this year.

They pursued that outcome, CNN has reported, around the same time they were working with Giuliani, President Donald Trump's personal attorney, to encourage Ukranian officials to investigate Trump's political rival, Democratic presidential candidate Joe Biden and his son, Hunter Biden. They were also actively pushing to have the US ambassador to Ukraine, Marie Yovanovitch, removed.

An American energy consultant who operates in Ukraine, Dale Perry, described the efforts to oust Naftogaz's CEO, Andriy Kobolyev, who is known for his anti-corruption reforms at the company. At an energy conference in Houston last March, Parnas and Fruman asked a senior Naftogaz executive Andrew Favorov if he would go along with their plan to oust the company's current CEO and become its head, according to Perry, who is Favorov's former business partner.

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