New York (CNN) Federal prosecutors investigating associates of Rudy Giuliani have focused on a Ukrainian state-owned natural gas company, a move that suggests authorities are exploring whether a law prohibiting the payment of bribes to foreign officials has been violated.

The fresh line of inquiry has accelerated in recent weeks. New York federal prosecutors have interviewed two senior executives at Naftogaz, the Ukrainian state-run energy company, and requested interviews with at least two others who are believed to have some knowledge of the alleged scheme by Giuliani's associates Lev Parnas and Igor Fruman to replace Naftogaz's chief executive in hopes of bettering their business prospects.

The questions connected to Naftogaz suggest prosecutors -- who have been investigating Parnas, Fruman and Giuliani as part of a broad inquiry that includes potential foreign lobbying violations -- are also looking at whether yet another law was violated, legal experts say. The law, called the Foreign Corrupt Practices Act, prohibits a US company or individual from giving any payment, offer of payment or anything of value to a foreign official in order to obtain or retain business.

A spokesman for the US attorney's office in Manhattan declined to comment.

The sequence of events surrounding Naftogaz appears to meet many of the elements necessary for a foreign bribery charge, according to former federal prosecutors. "Any time you have some international business angle, thoughts understandably turn to the Foreign Corrupt Practices Act," said Harry Sandick, a former prosecutor in the Manhattan US Attorney's office.

Parnas and Fruman were indicted in October on charges of violating campaign finance laws by funneling foreign money into US elections and disguising the true source of other donations. Since then, prosecutors have pursued a broader case that includes questions about Giuliani's role, and prosecutors and FBI agents have interviewed political donors and fundraisers and subpoenaed others seeking any communications they've had with Giuliani about actual or potential business deals.

According to one grand jury subpoena issued as part of the inquiry, prosecutors are exploring whether laws including money laundering, undisclosed foreign lobbying, obstruction of justice and wire fraud may have been violated. Prosecutors said last week that additional charges are "likely." The Soviet-born American businessmen have pleaded not guilty.

In the case of Naftogaz, Parnas and Fruman approached a senior executive at the company and offered to make him CEO in hopes of drumming up business from Naftogaz for their newly created liquified natural gas operation.

While making their pitch to the senior executive, Andrew Favorov, he has said, the two touted their ties to Giuliani and suggested US ambassador to Ukraine Marie Yovanovitch, whom they viewed as opposed to their interests, would soon be removed. Yovanovitch later lost her job at least in part as a result of a scheme conducted by Parnas and Fruman, according to prosecutors.

Favorov said he rejected the pitch. He and Naftogaz CEO Andriy Kobolyev have been interviewed by prosecutors, according to an attorney who represents both men.

Giuliani's role in the alleged attempted scheme isn't clear. When Parnas and Fruman approached Favorov about the deal, they began their meeting by showing him pictures of them with Giuliani and text messages exchanged with President Donald Trump's personal attorney while conveying to Favorov that "Rudy's on our team," according to a person familiar with the encounter.

This person added that Parnas and Fruman appeared to use Giuliani's name to try to bolster their credibility but Favorov was not given any indication that Giuliani was, in fact, involved in the business.

Prosecutors are exploring Giuliani's business ties with Parnas and Fruman and whether he had any connection to Global Energy Producers, their liquified natural gas company. Robert Costello, an attorney for Giuliani, has said he had no financial interests in GEP.

Around the same time, Ukrainians complained to US officials that Giuliani was pushing for changes to the supervisory board of Naftogaz while he also sought investigations of the Bidens, according to testimony during the House impeachment inquiry by Fiona Hill, the former top Russia expert on the National Security Council. There has been no evidence of wrongdoing by either Joe or Hunter Biden.

Regardless of whether Giuliani played any substantive role in Parnas and Fruman's pitch to replace the company's CEO, legal experts say their actions appear to contain the components for a foreign bribery charge.

One significant element of such a charge requires that the thing of value -- in this case, the CEO position -- be offered to a foreign official. Favorov is a US citizen, but because Naftogaz is state-owned, he would be considered a foreign official in the eyes of prosecutors, said Berit Berger, a former New York federal prosecutor who is now executive director of the Center for the Advancement of Public Integrity at Columbia Law School.

"DOJ has taken the position that employees of a state-owned business are foreign officials for the purpose of FCPA," Berger said. "I don't think it matters that he was an American citizen as long as he was conducting the business of Naftogaz."

Berger pointed out that the charge does not require that the thing of value actually have been given, merely that it was offered, making Favorov's rejection of the proposal irrelevant to whether Parnas and Fruman broke the law.

The charge also requires that the scheme has a nexus to the US, which former prosecutors said could be satisfied by the fact that Parnas and Fruman made their pitch at an energy conference in Houston, Texas, according to Favorov, as well as by the fact that Favorov is a US citizen.