A top US diplomat has told an impeachment inquiry that he followed President Donald Trump’s orders to put pressure on Ukraine to investigate his Democratic rival Joe Biden.

Ambassador Gordon Sondland said the instruction came from Mr Trump’s personal lawyer Rudy Giuliani.

The inquiry is assessing if Mr Trump withheld military aid to Ukraine as a precondition. He denies any wrongdoing.

It is illegal in the US to seek foreign help to gain electoral advantage.

Mr Biden is one of top contenders for the Democratic nomination for the 2020 presidential election.

Mr Giuliani specifically mentioned the company Burisma – which had the son of Democratic presidential candidate Mr Biden, Hunter, as a board member – and issues surrounding the 2016 US presidential election, he said.

If found guilty in a majority vote in the House, Mr Trump will face an impeachment trial in the Senate. But two-thirds of members of that Republican-controlled chamber would then need to vote for Mr Trump to be removed from office.

What exactly did Sondland say?

In his opening statement, Mr Sondland said he had worked with Mr Giuliani “at the express direction of the president”. While he is the US ambassador to the EU, Mr Sondland said his brief included work on Ukraine alongside other colleagues – despite that country not being an EU member.

He then confirmed that the president had sought an investigation in exchange for a White House visit for Mr Zelensky – a quid pro quo, meaning a favour in return for a favour.

However, Mr Sondland also said he had never directly heard from the president that military aid would be released in exchange for such a probe.

The US diplomat said he was “adamantly opposed” to the suspension of military aid to Ukraine, and was never told why it was withheld.

Who knew about the Ukraine plan?

Mr Sondland said the leaders of the state department, National Security Council and White House were informed, including Secretary of State Mike Pompeo. He does not remember any objections from his superiors to the policy.

The ambassador said he even discussed the fact military aid had been withheld with Vice President Mike Pence on a visit to Warsaw in September.

Who else did the panel hear from on Tuesday?

Deputy Assistant Secretary of Defence Laura Cooper and Undersecretary of State David Hale testified later on Wednesday.

Mr Hale said that in March he was “concerned” by a campaign of attacks in Ukraine against then-Ambassador Marie Yovanovitch and felt she needed a statement of support from the state department.

He told the hearing that he immediately briefed Secretary of State Mike Pompeo on the issue, but Mr Pompeo “did not issue a statement at that time”.

In May Ms Yovanovitch was recalled by President Trump, who called her “bad news” in his controversial phone call.