President Donald Trump’s allies are warning that British Prime Minister Andy Burnham’s appointment of Ed Miliband as foreign secretary could strain the U.S.-U.K. relationship, citing Miliband’s history of attacking Trump and his support for net-zero energy policies.

Burnham appointed Miliband on Monday, replacing Yvette Cooper and completing a remarkable political comeback for the former Labour Party leader. Miliband led Labour from 2010 until the party’s defeat in the 2015 general election and most recently served as energy security and net zero secretary under former Prime Minister Keir Starmer.

The appointment makes Miliband Britain’s top diplomat and a principal counterpart to Secretary of State Marco Rubio at a time when Burnham is seeking to preserve close ties with Washington. Burnham spoke with Trump shortly after becoming prime minister and reaffirmed the importance of the bilateral relationship, according to Reuters.

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The Daily Telegraph reported that Trump administration officials had warned Burnham’s team against giving Miliband a senior role. Steve Bannon, Trump’s former White House chief strategist and a political ally of the president, told the newspaper that the administration viewed Miliband’s appointment as "very injurious" to the special relationship. Bannon does not currently hold an administration position, and the White House has not publicly confirmed that such a warning was delivered.

The London Times separately reported before the appointment that the administration had signaled opposition to Miliband and was even more concerned about the prospect of him becoming foreign secretary. That reporting was not attributed to a named administration official.

Miliband has previously condemned Trump in unusually personal terms.

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During Trump’s first presidential campaign, Miliband described him as a "racist, misogynistic, self-confessed groper." The comment resurfaced after Trump won the 2024 election, when BBC Breakfast presenter Jon Kay questioned Miliband about how he would work with the incoming president.

"How are you going to build a relationship with someone you described in the past as a racist, misogynistic, self-confessed groper?" Kay asked during the Nov. 12, 2024, interview.

"I’ve said some things in the past," Miliband responded. "My job now as a government minister is to work with people."

The differences extend beyond Miliband’s rhetoric about Trump. As energy secretary, Miliband became the public face of the Labour government’s net-zero agenda and its opposition to issuing new licenses for North Sea oil and gas exploration. Trump and members of his administration have pushed Britain to increase domestic fossil-fuel production.

Nile Gardiner, director of the Margaret Thatcher Center for Freedom at the Heritage Foundation and a former foreign-policy aide to Prime Minister Margaret Thatcher, told Fox News Digital that Miliband’s appointment was a "disastrous" decision.

"I think the appointment of Ed Miliband as U.K. foreign secretary is disastrous for Britain," Gardiner said in an interview Tuesday. "It’s a demonstration of a real lack of strategic thinking on the part of Andy Burnham."

"Ed Miliband is no friend of the United States," Gardiner continued. "He has been an outspoken critic of President Trump. Miliband is also widely viewed by U.S. conservatives as the architect of the whole net-zero agenda, which is viewed as completely poisonous by the U.S. administration."

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Gardiner called the appointment a "very high-risk move" that "makes no sense."

"Burnham is already off to a very bad start with this appointment," he said. "I’m in no doubt there will be very significant tensions between President Trump and Prime Minister Burnham, and Miliband’s appointment is quite possibly the worst appointment that Burnham could make as foreign secretary."

As he delivered his first remarks following the appointment, Miliband mentioned his family’s experience as Holocaust survivors.

"It’s the honor of my life, being asked by the prime minister to be the foreign secretary of our country," Miliband said in a statement Tuesday. "My parents came here, Jewish refugees fleeing from the Nazis, and for them Britain provided sanctuary and a beacon of hope in the fight against fascism."

"At a time when the values of democracy, the rule of law and freedom are under threat as never before, I will carry that spirit, their spirit, into my work as foreign secretary," he said. "And now I’m going to go and get on with the task."

Miliband also pledged to nurture Britain’s "strong, enduring and essential alliance" with the United States while deepening its strategic relationship with the European Union, according to the Financial Times.

His appointment has also raised concerns among some British Jewish and pro-Israel commentators.

Stephen Pollard, a former editor and current columnist for The Jewish Chronicle, argued in an opinion piece published Tuesday that Miliband’s record as Labour leader, including changes to party leadership rules that preceded Jeremy Corbyn’s rise, should concern British Jews and supporters of Israel. Pollard predicted that the Burnham government would pursue additional sanctions against Israel with the support of a Jewish foreign secretary.

The Burnham government had not announced additional sanctions against Israel as of Tuesday.

Conservative Member of Parliament Priti Patel separately criticized Burnham and Miliband over plans to proceed with the Chagos Islands agreement.

"Burnham and Miliband are wrong to press ahead with Labour’s appalling Chagos Surrender," Patel wrote on X, arguing that the agreement would transfer British territory and cost taxpayers £35 billion (approximately $47 billion.)

"Once again, the same old Labour Party is undermining our national security and making Britain weaker on the international stage," she added.

On Monday, President Donald Trump said he spoke with Burnham shortly after he took office, calling the conversation "very good." Trump added that he and Burnham plan to meet in the "not too distant future" to discuss issues of mutual interest.

The White House, State Department, Miliband’s office and Burnham’s office did not immediately respond to Fox News Digital’s requests for comment.

Fox News' Bonny Chu contributed to this article.