Sally Yates, who was appointed by Barack Obama, ordered justice department lawyers not to enforce the president's executive order.

A White House statement accused Ms Yates of "betraying" the justice department and being "weak on borders".

Mr Trump replaced her with Dana Boente, US attorney for the Eastern District of Virginia.

Mr Boente said he was "honoured to serve President Trump" and immediately directed his department to enforce the controversial order.

Mr Trump also replaced the acting director of the US Immigration and Customs Enforcement, Daniel Ragsdale, who has been in the post since 20 January. He is the former deputy director.

No reason was given for Mr Ragsdale's sacking. He has been replaced by Thomas Homan, the executive associate director of enforcement and removal.

Mr Trump's order temporarily banned nationals from seven Muslim-majority countries from entering the US, and sparked street protests in the US and abroad.

Ms Yates, a career prosecutor who served as deputy attorney general under Barack Obama, said in a letter that she was "not convinced" that the president's order was lawful.

"As long as I am the acting attorney general, the department of justice will not present arguments in defence of the Executive Order," she said.

Within hours, the White House announced: "President Trump relieved Ms Yates of her duties."

A statement claimed she had "betrayed the department of justice by refusing to enforce a legal order designed to protect the citizens of the United States".

It also described her as "weak on borders and very weak on illegal immigration".

Democrats hits back at Ms Yates' dismissal. Senator Chuck Schumer, the party leader, said in a statement that the "attorney general should be loyal and pledge fidelity to the law, not the White House. The fact that this administration doesn't understand that is chilling".