Diplomat said he expressed concern over Hunter Biden’s foreign work in 2015

During a closed-door deposition earlier this week, a senior State Department official told House impeachment investigators that he raised ethical concerns about Hunter Biden’s business ties in Ukraine with then-Vice President Joe Biden’s office in 2015, two sources familiar with the deposition confirmed Friday to ABC News, but was ultimately rebuffed.

Deputy Secretary of State George Kent told investigators that he grew so concerned about the appearance of a conflict of interest presented by Hunter Biden’s role on the board of a Ukrainian oil and gas company that he conveyed his misgivings to an aide to the then-vice president, the sources said.

Kent said in his testimony that Biden’s aide told him that the vice president didn’t have the “bandwidth” to address Hunter Biden’s professional work because his other son, Beau, was battling cancer, according to the Washington Post, which first reported Kent’s claim.

A spokesman for House Intelligence Committee Chairman Adam Schiff, D-Calif., declined to comment on the closed door testimony. A spokesman for the Biden campaign said that "on Joe Biden's watch, the U.S. made eradicating corruption a centerpiece of our policies toward Ukraine."

In a statement from his lawyers on Friday, Kent, a career Foreign Service officer who previously served at the U.S. embassy in Kyiv, tried to distance himself from any of the politics: "Those engaged in the broader political debate on either side will likely find both utility and inconvenience in his testimony. But those are matters for others. He was not there to testify on behalf of any side," his lawyers Andrew Wright and Barry Hartman wrote.

Without disputing anything in particular, they added, "With varying degrees of accuracy, several news organizations and sources have characterized the testimony he provided in closed session. We would caution that cherry-picked elements of his testimony might not give the full picture."

At the time of Kent's warning, Joe Biden was routinely traveling to Kiev, to advocate the Obama administration policy focused on rooting out corruption. A year earlier, in 2014, Hunter Biden had accepted a lucrative seat on the board of directors for Burisma, the Ukrainian company.

While the Bidens have not been accused of doing anything illegal, ethics experts say Hunter Biden’s foreign business activity presents ethical concerns.

"At absolute minimum, there's a huge appearance of conflict, and there's every reason to think that the investors that he‘s working with want him partnering with them because he's the son of the then-vice president and now presidential candidate," Robert Weissman, president of progressive watchdog group Public Citizen, told ABC News in June. "[Joe Biden] should have encouraged his son to not take these positions."

During an exclusive interview with ABC News earlier this week, Hunter Biden said he exercised “poor judgment” in taking the Burisma board seat, but defended himself against the ethical questions raised about his private ventures,

"I gave a hook to some very unethical people to act in illegal ways to try to do some harm to my father. That's where I made the mistake," said Biden. "So I take full responsibility for that. Did I do anything improper? No, not in any way. Not in any way whatsoever."

Nevertheless, Kent’s testimony will likely add fuel to claims made by President Donald Trump and his allies about an alleged conflict of interest, who staged a full-court press to have the Hunter Biden and his father investigated in Ukraine. During a phone call in July between Trump and Ukrainian President Volodymyr Zelenskiy – a rough transcript of which the White House later released – the president repeatedly encouraged the Ukrainians to investigate the Bidens.

The president’s requests to Zelenskiy during that phone call are now a major part of the congressional impeachment inquiry. Investigators have interviewed several current and former United States officials as part of their probe, including Kent.

Although Trump’s effort to repeatedly raise Hunter Biden’s foreign business ties has brought them more into the spotlight recently, questions were raised at the time he took on the position in Ukraine. In May 2014, ABC News Chief White House Correspondent Jonathan Karl asked then-White House press secretary Jay Carney about the potential conflict of interest.

Carney responded that "Hunter Biden and other members of the Biden family are obviously private citizens, and where they work does not reflect an endorsement by the administration or by the vice president or president."

ABC News' Ben Siegel and Conor Finnegan contributed to this report.