Washington (CNN) Career diplomat George Kent told congressional investigators earlier this week he had voiced concerns in early 2015 about former Vice President Joe Biden's son Hunter working for a Ukrainian natural gas company, the Washington Post reported Friday.

Citing three people familiar with the testimony, the newspaper reported that Kent, the deputy assistant secretary of state for European and Eurasian affairs, recounted concerns during his testimony Tuesday that Hunter Biden's work could undercut American efforts to convey to Ukraine the importance of avoiding conflicts of interest.

The people told the Post when Kent raised the risk of Ukraine viewing Biden as a direct line to his father, he told investigators, the then-vice president's office responded that Biden didn't have the "bandwidth" to address Hunter's situation while his other son, Beau, battled brain cancer. Kent did not name the Biden staffer he interacted with, the people told the Post.

Andrew Bates, a spokesman for Joe Biden's presidential campaign, defended the former vice president's conduct in Ukraine.

"Donald Trump's unprecedentedly corrupt administration is melting down because of the scandal he touched-off by trying to get Ukraine to lie about Joe Biden -- and as the vice president said yesterday, he should release his tax returns or shut up," Bates said in a statement. "On Joe Biden's watch, the US made eradicating corruption a centerpiece of our policies toward Ukraine, including achieving the removal of an inept prosecutor who shielded wrongdoers from accountability."