Mark Esper
Mark Esper Image Credit: AFP

US President Donald Trump on Monday said Defense Secretary Mark Esper had been "terminated" and that Christopher Miller, director of the National Counterterrorism Center, will be acting Secretary of Defense starting immediately.

"Mark Esper has been terminated," Trump said on Twitter. "I am pleased to announce that Christopher C. Miller, the highly respected Director of the National Counterterrorism Center (unanimously confirmed by the Senate), will be Acting Secretary of Defense, effective immediately."

"Chris will do a GREAT job!'' Trump tweeted. "Mark Esper has been terminated. I would like to thank him for his service.''

Esper's strained relationship with Trump came close to collapse last summer during civil unrest that triggered a debate within the administration over the proper role of the military in combatting domestic unrest. Esper's opposition to using active duty troops to help quell protests in Washington, D.C., infuriated Trump, and led to wide speculation that the defense chief was prepared to quit if faced with such an issue again.

Officials familiar with internal discussions say Esper has been ready to resign for months, and as rumblings about Trump's unhappiness with him have grown, he's taken additional steps to prepare to step down.