The White House released a call transcript Wednesday confirming Donald Trump asked his Ukrainian counterpart to probe his political rival Joe Biden -- a day after Democrats seized on the explosive allegation to launch an impeachment process.

Democratic presidential hopeful Joe Biden makes a statement on Ukraine corruption during a press conference at the Hotel Du Pont on September 24, 2019, in Wilmington, Delaware. [Photo: AFP]

"There's a lot of talk about Biden's son, that Biden stopped the prosecution and a lot of people want to find out about that," Trump told Volodymyr Zelensky in the July 25 call.

As Barack Obama's vice president, Joe Biden and other Western leaders pressured Ukraine to get rid of the country's top prosecutor, Viktor Shokin, because he was seen as not tough enough on corruption.

"Biden went around bragging that he stopped the prosecution so if you can look into it," Trump said.