The US Secretary of Homeland Security Kirstjen Nielsen, who enforced some of President Trump’s controversial border policies, has resigned.
Ms Nielsen called it “an honour of a lifetime” to work in the department.
President Trump tweeted she would be temporarily replaced by Customs and Border Protection Commissioner Kevin McAleenan.
Ms Nielsen was responsible for implementing the proposed border wall and the separation of migrant families.
She gave no reason for her departure in her resignation letter, although she said this was “the right time for me to step aside” and said the US “is safer today than when I joined the Administration”.
The announcement she is leaving her post comes days 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 drugs and migrants crossing into the US.