Ukraine’s president has joked that the only person who can pressure him is his six-year-old son, amid a growing scandal over whether US leader Donald Trump leaned on Kiev to investigate a political rival.

“Nobody can pressure me because I am the president of an independent country,” Volodymyr Zelensky told the Russian news channel Rossiya 24 from New York.

“The only person who can put pressure on me is my son, who is six years old,” added the leader, who was a popular comedian before his surprise election to the presidency earlier this year.Zelensky and Trump are due to meet for the first time on Wednesday on the sidelines of the United Nations General Assembly.

US Democrats have launched a formal impeachment inquiry against Trump, accusing him of abuse of power over a reported attempt to pressure Zelensky into opening a corruption probe into ex-Vice President Joe Biden, the leading Democrat presidential contender.

The investigation the first step in a possible impeachment process allegedly would have focused on Biden’s son Hunter and his work for a Ukrainian company while his father was President Barack Obama’s deputy.Trump has admitted discussing Biden with Zelensky, but denied reports he threatened to suspend military aid in the case of refusal.