On Monday, President Donald Trump terminated Pentagon chief Mark Esper and announced Miller would serve as acting defence secretary.
"Today, Acting Under Secretary of Defence for Policy Dr James Anderson, Under Secretary of Defence for Intelligence and Security Mr. Joseph Kernan and Chief of Staff to the Secretary of Defence, Jen Stewart submitted letters of resignation", the release said on Tuesday.
Earlier on Tuesday, US media reported that Anderson decided to step down because of disagreements with the White House.
These resignations come a day after Trump announced he terminated Esper from his defence chief post, though earlier, Pentagon refuted claims about possible proved Esper's resignation.
The president is also reportedly expected to fire FBI Director Christopher Wray and CIA Director Gina Haspel.
