Donald Trump fires a second senior official who testified against him

US President Donald Trump has fired a second senior official who testified against him in the impeachment inquiry.

Gordon Sondland, the United States' ambassador to the EU, was ousted on Friday just hours after Lt. Col. Alexander Vindman who had worked as an expert on Ukraine at the White House.

Trump survived impeachment after the Republican dominated Senate voted in his favour on Wednesday.

"I was advised today that the President intends to recall me effective immediately as United States Ambassador to the European Union," Sondland said in a statement on Friday.

Lt. Col. Vindman had testified in impeachment hearings that he didn't think it was "proper" for Trump to "demand that a foreign government investigate" former Vice President Joe Biden and his son.

Vindman, who was born in Ukraine, turned up to work on Friday at the White House but was swiftly escorted out.

He has now been re-posted to the army, the US military said, but gave no further details.

Vindman received the prestigious purple heart medal for bravery after being injured by an improvised explosive device in Iraq.

"The truth is that it has cost the lieutenant colonel his job," said David Pressman, one of Vindman's lawyers, adding that he had no doubt that it was political revenge.

In his testimony, Vindman argued that he believed the then Ukrainian attorney general, Yuri Lutsenko, and Trump's personal lawyer, Rudy Guiliani, had "promoted a false narrative" that undermined US policy in Ukraine.

Commenting on own position in the White House he had stated that the military serves the country, and not "any particular political party."