Fiona Hill, the former top Russia expert on the National Security Council, arrives to testify  on Capitol Hill in Washington, DC. Photograph: Brendan Smialowski/AFP via Getty Images

A former adviser to US president Donald Trump has warned members of Congress not to propagate a debunked conspiracy theory that Ukraine interfered in (...)

 Lt Col Alexander Vindman testifies before the House intelligence committee  on Capitol Hill, in Washington, DC, US. Photograph: Chip Somodevilla/Getty Images

Two US officials who listened in to the July 25th phone call between president Donald Trump and Ukrainian president Volodymyr Zelenskiy have told the (...)

US president Donald Trump has called for the whistleblower to testify in person. Photograph: Chip Somodevilla/Getty Images

The impeachment investigation into president Donald Trump entered a new phase on Monday as House Democrats published full transcripts of the depositio(...)

Lt Col Alexander Vindman, the top Ukraine expert on the US National Security Council, arriving to speak with House impeachment investigators on Capitol Hill in Washington on Tuesday. Photograph: Anna Moneymaker/The New York Times

Lt Col Alexander Vindman, the top Ukraine expert on the National Security Council, told House of Representatives impeachment investigators on Tuesday (...)