US President Donald Trump has defended raising his political rival Joe Biden during a phone call with Ukrainian President Volodymyr Zelensky, as more Democrats call for impeachment proceedings. Mr Trump denied pressuring Mr Zelensky to investigate unsubstantiated corruption allegations against Mr Biden, but acknowledged mentioning the former vice-president in the context of corruption in Ukraine.
Democrats have accused Mr Trump of threatening to withhold $250m in military aid to Ukraine to pressure Mr Zelensky into investigating Mr Biden and his son Hunter. The claim has not been proven, but a top Democrat, Congressman Jim Himes, said the alleged attempt to pressure a foreign leader was an impeachable offence. "This really ups the ante," he told CNN.
Mr Trump and his allies have alleged that Mr Biden, as Barack Obama's vice-president, encouraged the firing of Ukraine's top prosecutor because the prosecutor was investigating Burisma, a gas company that employed Hunter Biden. Both Bidens deny any wrongdoing, and no evidence has been provided. The call coincided with a temporary freeze on military aid to Ukraine, which was later released after bipartisan criticism.
An intelligence whistleblower has filed a complaint about Mr Trump's promise to a foreign leader, but the administration has blocked it from being handed to Congress. The president called the whistleblower "partisan" and insisted he did nothing wrong. He suggested releasing a transcript of the call, but senior officials argued private conversations should remain confidential.
