The United States Ambassador to Greece, Kimberly Guilfoyle, has resigned following a series of misconduct allegations, including claims that she offered a political donor access to senior administration officials in exchange for money.

White House press secretary Katie Zacharia confirmed the departure on Tuesday. "We have asked ambassador Guilfoyle to resign," she told reporters. "She has been a wonderful asset to the team, and we wish her well."

Shortly after the announcement, Guilfoyle posted on social media confirming her resignation. "While my time as Ambassador may be coming to an end, my commitment to President Trump, the America First movement, and the country I love will never end," she wrote.

She denied all allegations against her. "These allegations are false, and I intend to vigorously defend my name, my reputation, and my integrity," she said.

According to reports, Guilfoyle asked a Trump donor to cover a $100,000 credit card bill shortly before her congressional confirmation hearing, promising him access to administration officials in return.

Reports also alleged that she told guests at a reception that she could use US influence to undermine the Greek government, promoted the interests of a Greek construction and energy company, and allowed one of its lobbyists to attend private diplomatic meetings.

Guilfoyle's lawyers have said the money she sought was payment for previous speaking engagements and public appearances for which she had not been compensated.

President Trump signalled on Monday that he was considering removing her from the post. "Well, we're looking at it," he told reporters. "We're not happy."

Secretary of State Marco Rubio initially defended Guilfoyle, calling her a "strong ambassador," but later declined to comment on the allegations and criticised reporters for raising them.

Guilfoyle is a former Fox News host and California prosecutor. She is the former wife of California Governor Gavin Newsom and was previously engaged to Trump's eldest son, Donald Trump Jr.