A top US diplomat told impeachment hearings that President Trump directly asked about a Ukrainian investigation into his Democratic rival Joe Biden.

In previously unheard testimony, Bill Taylor, the acting US ambassador to Ukraine, said a member of his staff was told Trump was preoccupied with pushing for a probe into Biden. He was speaking at the first public hearings in the impeachment inquiry. Trump told reporters he did not recall making such comments. Trump is accused of withholding US military aid to Ukraine in order to pressure the country's new president to publicly announce a corruption inquiry into Biden, among the favourites to take him on in the 2020 presidential race. Trump denies any wrongdoing and has called the inquiry a "witch-hunt". It is illegal in the US to ask foreign entities for help in winning an election.

What did Trump allegedly ask about?

During a detailed opening statement, Taylor said a member of his staff had overheard a telephone call in which the president inquired about "the investigations" into Biden. The call was with Gordon Sondland, the US ambassador to the European Union, who reportedly told the president over the phone from a restaurant in Kyiv that "the Ukrainians were ready to move forward". After the call, the staff member "asked ambassador Sondland what President Trump thought about Ukraine", Taylor said. Taylor said: "Ambassador Sondland responded that President Trump cares more about the investigations of Biden." Meanwhile observers and former officials have drawn attention to the security implications of making the call from a restaurant, potentially exposing the conversation to eavesdropping by Russian intelligence. When asked about  Sondland earlier this month, the president had said: "I hardly know the gentleman." Responding to queries from reporters after the hearing, Trump said: "I know nothing about that, first time I've heard it." He said he recalled Sondland's testimony, in which the diplomat said he spoke to the president "for a brief moment" and Trump had "said no quid pro quo under any circumstances". He did not recall the phone call Taylor described, "not even a little bit", and "in any event it's more second hand information", he said. The impeachment inquiry has been going on for more than a month - but all previous hearings were private, with reports based on leaks and sources speaking to the media. Wednesday's public hearings were the first time the public heard from witnesses directly and a chance for Democrats and Republicans to win over voters. BBC