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 U.S. President 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 Wednesday on the sidelines of the United Nations General Assembly (UNGA). 

Democrats in the U.S. House of Representatives on Tuesday launched a formal impeachment inquiry into Trump, accusing him of seeking Ukraine's help to smear Democratic rival Joe Biden ahead of next year's election. Trump has dismissed the inquiry as a witch hunt. 

The allegations turn on a July 25 telephone call between Trump and Zelensky during which critics allege Trump improperly pressured his Ukrainian counterpart to investigate Biden, the former U.S. vice president, and his son Hunter, who had worked for a company drilling for gas in Ukraine. 

Trump has said he did nothing wrong and that he'll release a transcript of the conversation later on Wednesday to prove it. 

Asked whether he would ask Trump for anything when they met, Zelensky said: "Asking for something is not Ukraine's style. It's a new strong country and isn't asking anyone for anything. We can help others ourselves." 

(Cover: The combination of pictures shows Ukraine's President Volodymyr Zelensky (L) in Paris, France, June 17, 2019, and U.S. President Donald Trump attends a meeting at the White House in Washington, D.C., U.S., September 20, 2019. /VCG Photo)

(With input from AFP, Reuters)