Washington (CNN) — Career diplomat George Kent told congressional investigators earlier this week he expressed concern 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, told concerns during his testimony Tuesday that hunter Biden’s work could undermine American efforts to communicate the importance of preventing conflicts of interest.

People told the post when Kent raised the risk of watching Biden as a direct line with his father, he told investigators, the then-Vice President’s office responded that Biden did not have the “bandwidth” to consider the situation hunter and his other son, Beau, were battling brain cancer. Kent did not name a Biden staffer he spoke with, people told the post.

Andrew Bates, a spokesman for Joe Biden’s presidential campaign, defended the former Vice President’s behavior in Ukraine.

“Donald trump’s unprecedentedly corrupt administration is melting over the scandal he touched on 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. “Before Joe Biden’s eyes, the U.S. has made eradicating corruption a Central element of our policy toward Ukraine, including removing the inept Prosecutor who shielded the abusers from accountability.”

CNN’s Sarah Mucha, Jeremy herb, Manu Raju and Marshall Cohen contributed to this report.