By Jake Tapper, Evan Perez and Betsy Klein, CNN

(CNN) -- United States Secret Service director Randolph "Tex" Alles is being removed from his position, multiple administration officials tell CNN.

President Donald Trump instructed his acting chief of staff, Mick Mulvaney, to fire Alles. Alles remains in his position as of now but has been asked to leave.

The USSS director was told two weeks ago there would be a transition in leadership and he was asked to stay on until there was a replacement, according to a source close to the director.

Secret Service officials have been caught by surprise with the news and are only finding out through CNN, according to the source.

In an email to employees at his agency obtained by CNN's Jim Acosta, Alles told the workforce he was not fired, but was told weeks ago that the administration would be making "transitions in leadership" at the Department of Homeland Security.

"The President has directed an orderly transition in leadership for this agency and I intend to abide by that direction," he wrote.

White House press secretary Sarah Sanders said later Monday that Trump has picked James M. Murray, a career USSS official, to replace Alles.

"United States Secret Service director Randolph 'Tex' Alles has done a great job at the agency over the last two years, and the President is thankful for his over 40 years of service to the country. Mr. Alles will be leaving shortly and President Trump has selected James M. Murray, a career member of the USSS, to take over as director beginning in May," she said.

A source familiar with the director said his ouster was not related to the recent scrutiny the Secret Service got after a Chinese woman illegally entered the President's Mar-a-Lago club carrying Chinese passports and a flash drive containing malware.

Just five days ago, Trump said he "could not be happier with Secret Service" following the Mar-a-Lago incident.

"Secret Service has done a fantastic job from Day 1. Very happy with them," Trump said during a White House event when asked by reporters about the Mar-a-Lago trespasser.

The Secret Service director reports directly to the Secretary of Homeland Security, Kirstjen Nielsen, who resigned on Sunday amid growing pressure from the President. The director oversees the Secret Service's work on both protection and investigations.

"There is a near-systematic purge happening at the nation's second-largest national security agency," one senior administration official says.

United States Citizenship and Immigration Services director Francis Cissna and Office of the General Counsel's John Mitnick are expected to be gone soon, and the White House is eyeing others to be removed.

The President in recent weeks empowered Stephen Miller to lead the administration's border policies "and he's executing his plan" with what amounts to a wholesale decapitation or the Department of Homeland Security leadership, the official says.

Alles previously served in Customs and Border Protection leadership and also led that agency's Air and Marine Operations. He is a 35-year veteran of the Marine Corps.

CNN's Pamela Brown, Jim Acosta, Jeremy Diamond and Allie Malloy contributed to this report.