The US Secretary of Homeland Security Kirstjen Nielsen, who enforced some of President Trump's controversial border policies, has resigned, the BBC reports.
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".
Its been an honor of a lifetime to serve with the brave men and women of @DHSgov. I could not be prouder of and more humbled by their service, dedication, and commitment to keep our country safe from all threats and hazards. pic.twitter.com/lIQ5iqGDmF— Sec. Kirstjen Nielsen (@SecNielsen) April 7, 2019