WASHINGTON (REUTERS) - Ukrainian Foreign Minister Vadym Prystaiko on Saturday (Sept 21) denied suggestions that US President Donald Trump had put pressure on Ukrainian leader Volodymyr Zelenskiy during a phone call in July.

In an interview with media outlet Hromadske, Prystaiko said Ukraine was an independent state and would not take sides in US politics even if "in theory" the country was in a position to do so.

He added that Kiev appreciated the assistance it received from Washington.

On Friday, reports by US media outlets said Trump repeatedly pressured Ukraine's president to investigate Joe Biden, one of Trump's chief political rivals, in a July phone call.

The call featured in a classified whistleblower complaint that has sparked a political battle between Democrats warning of a national security threat and Republicans turning it into an attack on Biden, a frontrunner in the field of Democrats seeking to challenge Trump in the 2020 presidential election.

Reuters has not confirmed details of the whistleblower's complaint. But a source familiar with the matter said it alleged "multiple acts" by Trump, not just a phone call with a foreign leader. The source requested anonymity because of the sensitivity of the issue.

Zelenskiy's office has so far declined to comment on the allegations.

"I know what the conversation was about and I think there was no pressure," Prystaiko said.

"This conversation was long, friendly, and it touched on many questions, sometimes requiring serious answers."

Trump dismissed the Sept 12 complaint from the whistleblower within the intelligence community as a partisan hit against him.

Trump had spoken to Zelenskiy less than three weeks before the complaint was filed. Trump is due to meet Zelenskiy during a United Nations gathering in New York.

Prystaiko said Zelenskiy had the right to keep conversations with other leaders confidential.

"I want to say that we are an independent state, we have our secrets," he was quoted as saying in the interview.

The July 25 call between the leaders is under investigation by three Democratic-led House committees, who want to know if Trump and his personal lawyer, Rudolph Giuliani, tried to pressure the Ukrainian government into aiding Trump's re-election campaign.

The Wall Street Journal reported on Friday that Trump urged Zelenskiy about eight times during the call to work with Giuliani to investigate Biden and Biden's son.