The third day of public impeachment hearings featured testimony from witnesses who listened to a key phone call in which Donald Trump asked for a 'favour' from Ukrainian president Volodymyr Zelenskiy.

'What I heard was inappropriate,' said Lt Col Alexander Vindman. 'It was improper for the president to demand an investigation into a political opponent.'

A witness requested by Republicans also backfired as Kurt Volker, a former special envoy to Ukraine, revised his earlier testimony and called allegations against Joe Biden 'self-serving and not credible'.