WASHINGTON, Oct. 15 (Xinhua) -- U.S. Democratic presidential candidate Joe Biden on Tuesday denied wrongdoing in his dealings with Ukraine, once again pushing back against President Donald Trump's reasoning for investigating him.

"My son did nothing wrong. I did nothing wrong," Biden said when asked at the Democratic presidential debate held in Westerville, Ohio, whether it was appropriate for his son Hunter Biden to serve on boards of foreign companies while he was the vice president of the United States.

Trump in a July 25 phone call with Ukrainian President Volodymyr Zelensky asked the Ukrainian leader to investigate the Bidens, accusing them of involvement in a corruption case against Burisma Holdings, a Ukrainian gas company where Hunter Biden once served as a board member.

The Trump-Zelensky phone call has prompted an impeachment inquiry into Trump led by House Democrats, who believed what the president said during the call -- and administration officials' interactions with the Ukrainian authorities before and after the call -- constituted efforts to solicit foreign help to interfere in the 2020 U.S. election.

In an interview with ABC News' "Good Morning America" on Tuesday, Hunter Biden regretted "poor judgement" on his part when recalling his experience at the Ukrainian company. He, however, insisted that he did nothing wrong, adding "did I make a mistake based upon some ethical lapse? Absolutely not."

Reacting to the ABC interview, Trump tweeted earlier Tuesday that "Hunter Biden was really bad on @GMA," adding that Joe Biden "has real problems!"

A lawyer of Hunter Biden's said in a statement Sunday that the junior Biden would "agree not to serve on boards of, or work on behalf of, foreign-owned companies" if his father is elected president.

The 12 Democratic candidates at the debate nearly unanimously supported the impeachment proceedings against Trump.