WASHINGTON, DC - Former U.S. Vice President Joe Biden's son on Sunday rejected claims of wrongdoing in relation to his business interests in Ukraine and China.

Hunter Biden was responding to claims by U.S. President Donald Trump about his business dealings, and Mr Trump's efforts to have other countries, including Ukraine investigate his activities.

Mr Trump, who is being challenged by Joe Biden for the presidency in the 2020 elections has become embroiled in impeachment proceedings because of his engagement with other countries over the dealings of a rival candidate's son.

Last week the president accused Hunter Biden of being kicked out of the U.S. Navy Reserve in 2013 for using cocaine.

On the weekend President Trump escalated his attacks, making them personal. "Hunter, you know nothing about energy," he said in a tweet. "You know nothing about China. You know nothing about anything, frankly. Hunter, you're a loser."

In another tweet on Sunday, the president posted: "Where's Hunter? He has totally disappeared! Now looks like he has raided and scammed even more countries!"

A lawyer, George Mesires, acting for Hunter Biden released a statement on Sunday addressing the accusations and abuse.

He said while Hunter was a board member of the Burisma energy company in Ukraine for 5 years, no foreign or domestic law enforcement agency accused him of any wrongdoing.

He left the Burisma board in April and said he would leave the board of China's BHR (Shanghai) Equity Investment Fund Management Company at the end of this month.

He was being paid up to $50,000 a month as a director of Burisma. Mesires, said he was n ot being paid any remuneration for his role with the Chinese investment firm but 2 years ago he took a 10% equity stake in the company which cost him $420,000. Biden jnr.'s lawyer said he had yet to get a return on his investment.

"Hunter undertook these business activities independently," Mesires said. "He did not believe it appropriate to discuss them with his father, nor did he."

Mesires said that when Hunter Biden "engaged in his business pursuits, he believed he was acting appropriately and in good faith."