US President Donald Trump has announced Secretary of Homeland Security Kirstjen Nielsen is leaving her position.
In a tweet, the president thanked her for her service and said she would be temporarily replaced by Customs and Border Protection Commissioner Kevin McAleenan.
Ms Nielsen has held her position since December 2017.
She has drawn criticism for her staunch defence of some of Mr Trump’s most contentious border policies.
Her department was responsible for implementing the proposed border wall and the separation of migrant families, and she became the face of the controversial moves.
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Last June, protesters booed Ms Nielsen as she ate at a Mexican restaurant in Washington DC.
But she brushed off the demonstration, tweeting that she would “work tirelessly” to fix the “broken immigration system”.
Members of the Democratic party have already commented on her departure, with Massachusetts Senator Ed Markey calling the move “long overdue”.
Her relationship with Mr Trump is said to have been difficult, although in public she has been unwaveringly loyal to the administration.
On Saturday Ms Nielsen tweeted that she “could not be more proud” of border patrol agents, praising their “compassionate, humanitarian response” to border security.
The announcement she is leaving her post comes the day after the president visited the southern border.
Mr Trump has recently threatened to shut the crossing, but has since backtracked and promised to give Mexico a year to stop illegal drugs and migrants crossing into the US.
The president insists the situation on the southern border is a crisis and has declared a national emergency, bypassing Congress to secure funds for his border wall plan.
Democrats have protested the move, and declared the emergency unconstitutional.
In March the Pentagon authorised the transfer of $1bn (£758m) to army engineers for construction.