Sally Yates, who had been appointed under President Barack Obama, earlier ordered justice department lawyers not to enforce the president’s executive order.
Dana J. Boente, US attorney for the Eastern District of Virginia, replaced Sally Yates as acting attorney general.
He has directed the department to enforce Donald Trump’s order.
In a statement, the White House said Sally Yates had “betrayed” the department.
Donald Trump’s order temporarily banned nationals from seven Muslim-majority countries from entering the US, and sparked street protests in the country and abroad.
In a letter, Sally Yates had said she was “not convinced” that the president’s order was lawful.
She said: “As long as I am the acting attorney general, the department of justice will not present arguments in defense of the Executive Order.”
Within hours, the White House announced: “President Trump relieved Ms Yates of her duties.”
Sally Yates had “betrayed the department of justice by refusing to enforce a legal order designed to protect the citizens of the United States”, a statement from the press secretary said.
The statement also described her as “weak on borders and very weak on illegal immigration”.
Sally Yates’ replacement, Dana Boente, was also appointed by Barack Obama, in 2015. He was confirmed by the US Senate – making him eligible for appointment while President Trump waits for his own nominee to be approved.
Senator Jeff Sessions is awaiting a confirmation hearing for the role later this week.
Meanwhile, hundreds of diplomats and foreign servants have been drafting a “dissent cable” to formally criticize Trump’s executive order.
A draft version of the cable said that immigration restrictions will not make the US safer, are un-American and will send the wrong message to the Muslim world.
The ban bars citizens from Iraq, Syria, Iran, Libya, Somalia, Sudan and Yemen.
The White House has consistently defended Donald Trump’s executive order despite the controversy, with press secretary Sean Spicer saying diplomats should “get with the program”.
In addition, former President Barack Obama has apparently broken with the convention of former presidents avoiding comment on their successors.
Commenting on the protests about the immigration order, Barack Obama said he was “heartened”.
In a statement, which did not mention Donald Trump by name, Barack Obama said: “Citizens exercising their constitutional right to assemble, organise and have their voices heard by their elected officials is exactly what we expect to see when American values are at stake.”
Donald Trump also replaced the acting director of the US Immigration and Customs Enforcement, Daniel Ragsdale, who has been in the post since January 20. He is the former deputy director.
The president appointed Thomas Homan, the executive associate director of enforcement and removal, as the new acting director.
A statement from the Department of Homeland Security announcing the change did not explain the reason for it.
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