DONETSK, Ukraine — U.S. Vice President Joe Biden's youngest son has joined the board of a gas company owned by an ally of Ukraine's fugitive ex-president Viktor Yanukovych and a key European interlocutor with Kiev who was previously president of Poland.

The move raises questions about a potential conflict of interest for Joe Biden, who was the White House's main interlocutor with Yanukovych while the latter was president and has since spearheaded Western efforts to wean Ukraine off Russian gas.

Company documents in Cyprus show that Joe Biden's son, R. Hunter Biden, became a member of the board of directors of Burisma Holdings, which describes itself as Ukraine's largest private natural gas producer, on April 18. Burisma announced Hunter Biden's appointment in a press release Monday on its website which was quickly picked up by Russian state media.

"Burisma's track record of innovations and industry leadership in the field of natural gas means that it can be a strong driver of a strong economy in Ukraine," Hunter Biden said in the statement on Burisma's website. "As a new member of the Board, I believe that my assistance in consulting the Company on matters of transparency, corporate governance and responsibility, international expansion and other priorities will contribute to the economy and benefit the people of Ukraine."

Hunter Biden could not be immediately reached for comment. An assistant at Rosemont Seneca Partners, the investment firm where he is partner, said he was out of the office. A woman who answered the phone at the London number listed for Burisma on its website appeared to have no idea who either Biden was. By late Tuesday, however, Burisma had reacted quickly enough to remove a link to a New York Times story from April, when Biden visited Kiev and urged it to reduce its dependence on Russian gas, from a prominent position on the homepage.

Kendra Barkoff, a spokesperson for Joe Biden, denied to comment on the vice president's son's appointment. "Hunter Biden is a private citizen and a lawyer," she said. "The Vice President does not endorse any particular company and has no involvement with this company."

It proved difficult to discern at first whether the Burisma website carrying the press release was even real. Its photos of Hunter Biden and Rosemont co-founder Devon Archer, who is listed as a member of the Burisma board, are lifted from Rosemont's website. The company site carries a bizarre interview with Archer — apparently first published in the Ukrainian newspaper Kapital, then translated badly into English with Slavic syntax left intact — in which he tacitly acknowledges his connections to the Biden family and says Burisma "reminds [him] of Exxon in its early days." The Burisma site was registered anonymously through the domain service GoDaddy in 2010, according to the who.is service.

Company registration documents for Burisma show, however, that both Hunter Biden and Archer joined its board of directors in April. Burisma is completely owned by another Cypriot offshore company, Brociti Investments Limited, which, records show, belongs to Mykola Zlochevsky, who was energy minister and deputy national security council chair under Yanukovych, deposed in February. While in government, Zlochevsky claimed that he had sold his energy assets, though an investigation in Ukrainian Forbes later showed this was untrue.

As well as the other directors listed on Burisma's website, Cypriot records list a man named Aleksander Kwasniewski — the name of Poland's president from 1995 to 2005 — as having become a director Jan 2. Kwasniewski was a key figure in the European Union's attempts to draw Ukraine closer to Brussels during Yanukovych's presidency: he and former European Parliament president Pat Cox visited Kiev 27 times in failed attempts to secure the release of Yanukovych's rival, former prime minister and current presidential candidate Yulia Tymoshenko, from prison.

While it was not immediately possible to confirm that the Burisma director was the same Kwasniewski, the address provided in the company documents, Wilanowska 5/2 in Warsaw, matches addresses provided for Kwasniewski's wife Jolanta's real estate company, Royal Wilanow Agency, according to Polish media reports. Other Polish media reports list the address as the Kwaniewski family's private apartment. Jolanta Kwasniewska left the firm while her husband was in office, but returned to manage it after his term ended.

Kremlin spokesperson Dmitry Peskov told BuzzFeed that Russia saw no conflict of interest in Joe Biden working to wean Ukraine off Russian gas - which makes up about 60 percent of the country's energy supply - while his son worked in the Ukrainian gas industry.

"Anyway, as everyone knows, there's no gas in Ukraine," he added. "The gas in Ukraine is Russian."

Rosie Gray contributed reporting from Washington, DC.