The US ambassador to Estonia is resigning, reportedly in frustration at remarks made by President Donald Trump about America's European allies.
James D Melville revealed in a Facebook post that Mr Trump's comments had brought forward his decision to retire, Foreign Policy magazine reported.
The US president has imposed trade tariffs on some EU industries and strongly criticised Nato allies.
Other US diplomats have also left their posts early in recent months.
In January, US ambassador to Panama John Feeley resigned saying he was no longer able to serve under President Trump.
A month earlier, Elizabeth Shackelford resigned from her post in Nairobi where she worked for the US mission to Somalia.
In her letter of resignation to then Secretary of State Rex Tillerson, she said she was quitting because the US had abandoned human rights as a priority, Foreign Policy reported.
In the private Facebook post seen by Foreign Policy, Mr Melville reportedly told friends: "For the president to say the EU was 'set up to take advantage of the United States, to attack our piggy bank', or that 'Nato is as bad as Nafta [the North American Free Trade Agreement]' is not only factually wrong, but proves to me that it's time to go."
Mr Melville is a career diplomat and took up his position as ambassador in Estonia in 2015 after being nominated by then President Barack Obama.
He had previously held senior diplomatic posts in several European countries and speaks Russian, German and French, according to his biography on the US State Department website.
A State Department spokesperson confirmed Mr Melville's departure on Friday, saying: "Earlier today, the United States' Ambassador to Estonia, Jim Melville, announced his intent to retire from the Foreign Service effective July 29 after 33 years of public service."
President Trump reiterated his criticism of fellow Nato members on Friday while on a flight from Washington to his private golf club in New Jersey.
He told reporters on board Air Force One that countries including Germany, Spain and France had to increase their financial contributions to the bloc.
"It's not fair what they've done to the United States," he said. "The United States is paying much more disproportionately to anyone else."
His remarks come less than two weeks before a Nato summit in Brussels.
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