U.S. President Donald Trump on Sunday confirmed he did discuss former vice president Joe Biden and corruption allegations in a phone call with Ukraine's leader, as Trump's opponents called for his impeachment. 

A whistleblower's complaint sparked off accusations that Trump had sought to persuade Ukrainian President Volodymyr Zelensky to provide damaging information on Biden, Trump's possible 2020 election challenger. 

Trump confirmed that the conversation, held in July, had addressed alleged corruption involving Biden and his son Hunter, and he floated the possibility that a transcript could be released.

"We had a very great conversation, very straight, very honest conversation. I hope they can put it out," Trump said, repeating that he had done nothing wrong. 

"The conversation I had was largely congratulatory, was largely corruption... and largely the fact that we don't want our people, like vice president Biden and his son, creating... the corruption already in the Ukraine." 

The Wall Street Journal reported that Trump pressed Zelensky about eight times on the call to investigate possible corruption involving Hunter, who worked with a Ukrainian natural gas company while his father was vice president. 

Biden told reporters on Saturday that Trump's actions appeared "to be an overwhelming abuse of power."

"I know what I'm up against, a serial abuser. That's what this guy is," Biden said.

The Democratic Party has been split on whether to push for impeachment proceedings against Trump since he came to power in 2017. 

But influential congressman Adam Schiff, chairman of the House Intelligence Committee, on Sunday said that his own reservations about impeachment were fading over Trump's Ukraine call. 

"We're talking about serious or flagrant abuse and potential violation of law," Schiff told CNN, calling for full disclosure of any "illicit conduct of the president of the United States and the added element of a cover-up." 

"I have been very reluctant to go down the path of impeachment (but) the president is pushing us down this road." 

Other legislators have called for Democratic leadership to pursue impeachment immediately, but House Speaker Nancy Pelosi, the Democratic leader in the House of Representatives, has so far resisted calls to formally begin the process. 

In a letter to colleagues later on Sunday, Pelosi warned the administration against keeping the details of the whistleblower complaint secret. The administration has so far resisted sharing the details of the complaint with lawmakers.

"If the administration persists in blocking this whistleblower from disclosing to Congress a serious possible breach of constitutional duties by the president, they will be entering a grave new chapter of lawlessness which will take us into a whole new stage of investigation," Pelosi wrote. 

The allegations echo the ongoing row over Russian meddling in the 2016 U.S. election when Trump defeated Hillary Clinton. 

Secretary of State Mike Pompeo told ABC that "if vice president Biden behaved inappropriately, if he was protecting his son and intervened in a way that was corrupt, I think we need to get to the bottom of it." 

Pompeo said it was up to White House whether to release the transcript. 

Trump and Zelensky will meet for the first time Wednesday at the UN General Assembly in New York. 

(With input from AFP, Reuters)