US President Donald Trump has fired his ambassador to Greece Kimberly Guilfoyle over a string of misconduct allegations, including that she pushed a top donor to pay off her huge credit card debt.

Her departure was announced by Trump’s new press secretary Katie Zacharia at her eyebrow-raising debut media briefing, which lasted only 14 minutes and allowed just three questions from reporters.

“We have asked ambassador Guilfoyle to resign,” said Zacharia, who replaces Karoline Leavitt, at the White House media conference.

“She ‌has been a ‌wonderful ⁠asset to the team, and we ​wish her well.”

Guilfoyle insisted she would “vigorously defend herself” while confirming that she would resign.

Guilfoyle is a former Fox News channel host and California prosecutor who was once married to California’s Democratic governor Gavin Newsom and was engaged to Trump’s son Donald Jr.

Trump had said on Monday (US time) that he was considering firing Guilfoyle, telling reporters: “We’re not happy.”

On Tuesday (US time), the administration said it had asked her to leave her post after she faced severe criticism over allegations she engaged in improper and possibly illegal conduct before and during her tenure in Athens.

US lawmakers previously expressed concerns ⁠over allegations that ‌Guilfoyle may ​have threatened to use US influence ​to undermine the Greek ‌government.

In a series of stories dating to late last month, the Wall Street Journal has reported questionable conduct by Guilfoyle, including an alleged threat to a host country official, accepting improper gifts and services and offering to use her influence inside the Republican administration in return for the payment of a large credit card bill.

Guilfoyle has not addressed the reports directly.

But in a statement released late on Sunday, her lawyers denied she had done anything wrong and claimed that the money she was seeking from a Trump donor was payment for services — public appearances and speaking engagements that predate her ambassadorial nomination — that had not been paid.

The lawyers also rejected allegations of impropriety related to Guilfoyle’s travel on private planes, saying that before every such trip she “sought, obtained and followed State Department guidance and followed the Department’s travel regulations”.

Ahead of Tuesday’s announcement, Greek opposition parties had called on the foreign ministry to summon Guilfoyle to respond to the allegations made against her.

“This, most importantly, is an issue of national dignity,” Sia Anagnostopoulou, a former deputy foreign minister, said in parliament on Friday.

Foreign Minister Giorgos Gerapetritis responded that Guilfoyle had been treated “the same way as every other ambassador” and argued that an official summons had not been necessary.

White House ‘unimpressed’ at new press sec

White House press secretary Katie Zacharia at her first media briefing. Photo: AAP

Trump’s new press secretary raised eyebrows at her first media briefing, which lasted a bare 14 minutes, with just three questions allowed.

Katie Zacharia was a former communications adviser at Trump Media & Technology Group – the company that owns Truth Social.

Zacharia appeared nervous in front of the White House press pack, fumbled her words and was unable to answer certain questions.

She replied “I’ll have to get back to you on that” when asked if the US had stopped sharing intelligence with Ukraine.

Zacharia spent eight minutes reading a script praising Trump, and accidentally called her husband “my president”.

Then she abruptly ended the briefing: “I am going to end it because President Trump is heading out to Marine One for our historic trip to Alaska, and we can ask him all of the questions out there”.

A number of media identities criticised Zacharia, but Trump said she was “very good”.

US news station MS Now reported that the Trump administration was “severely unimpressed” with her performance.

“She needs to get much better, fast, otherwise she’ll break Scaramucci’s record”, White House officials reportedly told the network.

Anthony Scaramucci lasted 11 days as Donald Trump’s press secretary in 2017.

-with AAP/Reuters