Marco Rubio, the US secretary of state, brushed off reporters’ questions about recent reports that Kimberly Guilfoyle, the US ambassador to Greece and Trump family ally, used her position to advance personal interests.

Rubio refused to respond to the latest allegations against Guilfoyle, raised in a Wall Street Journal report, claiming she asked a Trump donor to pay her $100,000 American Express bill in exchange for access to the administration, before her US Senate confirmation hearing.

“You guys somehow walk around thinking that because some source told you something, and you reported it, it’s the gospel. It’s not the gospel, it’s not the gospel for me,” Rubio told reporters while visiting Athens on Wednesday.

Rubio refused to answer questions regarding Guilfoyle’s reported conduct, the second report of its kind, instead saying “our embassy here is doing a great job” and “our ambassador has been a strong ambassador here”.

The top Democrats on the House foreign affairs and Senate foreign relations committees have asked Rubio to open an investigation into Guilfoyle’s conduct as an ambassador, though it is unclear whether this has happened.

A lawyer for Guilfoyle told the newspaper that she was “owed a balance” for travel and speaking at events before her nomination. Deters told the Wall Street Journal that he did not owe Guilfoyle any balance.

Concerns about Guilfoyle’s conduct were first raised in September when the Wall Street Journal reported she had used her position to invite Greek lobbyists to sit in on official diplomatic meetings and promoted the business interests of one particular Greek construction and energy company.

Senator Jeanne Shaheen, the ranking Democrat on the Senate foreign relations committee, sent a letter to Rubio on Tuesday, asking him to look into the allegations against Guilfoyle.

“Such actions do not serve US credibility overseas and risk undermining US diplomacy,” Shaheen wrote. “In advance of your upcoming travel to Greece, I request an immediate review of Ambassador Guilfoyle’s actions and a clarification of what steps have and will be taken to avoid undue influence and even the appearance of a conflict of interest.”

Separately, Gregory Meeks, the ranking Democrat on the House foreign affairs committee, sent a letter to Rubio in September, requesting more information about Guilfoyle’s conduct, her relationship with the Greek construction and energy company and her relationship with the lobbyist.

“If these reports are accurate, Ambassador Guilfoyle is unfit to represent the United States abroad and should be removed from her position,” Meeks wrote.

Guilfoyle, 57, was once a member of the Trump family’s inner circle, having been engaged to Donald Trump Jr, the US president’s eldest son, for roughly three years. The couple ended their engagement in 2024, and shortly after taking office, Donald Trump nominated Guilfoyle to be ambassador to Greece.

But now further allegations accuse Guilfoyle of promising a Trump donor, Eric Deters, access to the Trump administration in exchange for a $100,000 payment to American Express.

Deters shared messages exchanged between himself and Guilfoyle with the Wall Street Journal in which she reportedly pleaded: “Honey please I need you to get this done for me today.”

Deters said Guilfoyle had promised himshe would “be your Trump ride or die, forever and ever” if he made the American Express balance. Deters said he never made the payment.

A lawyer for Guilfoyle disputed the authenticity of messages Deters shared with the Wall Street Journal.

It is unclear whether Shaheen or Meeks will ask Rubio for further information about the latest report. The Guardian has asked Meeks and Shaheen for comment.