Image copyright EPA Image caption Ukrainian President Volodymyr Zelensky has denied being blackmailed

Ukrainian President Volodymyr Zelensky has said there was "no blackmail" in a phone call with Donald Trump that is at the heart of a possible attempt to remove the US president from office.

"This is not corruption, it was just a call," Mr Zelensky said on Thursday.

The call prompted a whistleblower complaint and Democratic impeachment inquiry of the Republican president.

Mr Trump denies withholding US aid while pressuring Ukraine to investigate political rival Joe Biden.

Impeachment is a process by which Congress can vote to oust a president - though it requires support from a majority of both chambers and as such, is currently thought unlikely to pass the Republican-controlled Senate.

Speaking to reporters at a news conference in Kiev on Thursday, Mr Zelensky said of his 25 July call with Mr Trump: "There was no blackmail. It was not the subject of our conversation."

He said the purpose of the conversation was to arrange a meeting with Trump, and there were no "conditions" from the American side.

Mr Zelensky also said he does not believe US-Ukraine relations will be affected by the impeachment inquiry.

A rough transcript of the call released by the White House shows Mr Trump asked Mr Zelensky to investigate Joe Biden, now a Democratic frontrunner for next year's White House election.

His son, Hunter Biden, landed a lucrative board position in 2014 with a Ukrainian gas firm, Burisma, that found itself under scrutiny from a former prosecutor general.

As US vice-president Mr Biden, like other Western officials, put pressure on Ukraine in 2016 to have the prosecutor fired, citing corruption concerns.

Mr Trump has said Mr Biden did so in order to derail the inquiry into Burisma. Ukrainian officials have said there is no evidence of wrongdoing by the Bidens.

The whistleblower who filed a complaint over the call said in a memo that a White House official who listened to the phone discussion described it as "crazy" and "frightening", US media report.

The official was "visibly shaken by what had transpired" in the call, the whistleblower reportedly wrote in the memo.

Media playback is unsupported on your device Media caption What we know about Biden-Ukraine corruption claims

On Wednesday a poll by Fox News, which is generally supportive of the president, found that 51% of voters are in favour of impeaching Mr Trump and removing him from office.

The results show 85% of Democrats were in favour of impeachment, while 82% of Republicans were against it.

Mr Trump hit back at Fox's poll results on Twitter, writing "whoever their pollster is, they suck".

Later on Thursday, the president is hosting his first rally since the launch of the impeachment inquiry, in Minneapolis, Minnesota.

Protests are expected against Mr Trump, who lost the state by a narrow margin to Hillary Clinton in 2016.

What do we know about the whistleblower?

The whistleblower whose complaint fuelled the impeachment inquiry had a "prior working relationship with a current 2020 Democratic contender" and is a registered Democrat, a source familiar with the matter told CBS News on Thursday.

The details of this working relationship or the candidate are unclear.

Lawyers representing the anonymous whistleblower said in a statement their client "has never worked for or advised a political candidate, campaign or party".

They also noted that as a government employee, their client has interacted with candidates from both parties "in their roles as elected officials - not as candidates".

The whistleblower's identity has remained a secret, though US media have reported he or she is a CIA officer.