The Pentagon chief of staff Kevin Sweeney has resigned from his position less than a month after US President Donald Trump announced that American forces would leave Syria.
He follows his boss Defence Secretary James Mattis out of the Department of Defence after he resigned last month in protest at the move and his decision to halve troop numbers in Afghanistan.
Rear Admiral Sweeney said in a statement that "the time is right to return to the private sector". He was in the post for two years and called it an "honour to serve" in the position. Department spokeswoman Dana White also resigned after the Syria announcmeent.
Mr Trump has faced criticism for his decision to withdraw from Syria over fears that ISIS or Iran will fill the vacuum left by US troops.
While the president appeared to suggest a rapid withdrawal, the pace of the American exit has appeared to have slowed, with officials briefing that the US is not going anywhere and that any withdrawal of some troops would be managed carefully.
Mr Mattis criticised the president upon leaving office, writing a letter that talked about "treating allies with respect" after the perceived betrayal of Kurdish allies in northern Syria.
Mr Trump said on Friday a New York Times report that he was considering former Democratic Senator Jim Webb to be his next defense secretary was "fake news".
The Times, citing an unnamed official, said on Thursday that Vice President Mike Pence and acting White House Chief of Staff Mick Mulvaney had reached out to Webb. A senior Pentagon official confirmed Webb's name had been circulating at the White House, the Times reported.
"I’m sure he is a fine man, but I don’t know Jim, and never met him," Mr Trump said on Twitter. "Patrick Shanahan, who is Acting Secretary of Defense, is doing a great job!" he said.
Mr Mattis stepped down from his job as defense secretary on Tuesday and Mr Trump said a day later he had essentially fired Mattis, a retired Marine general whose letter of resignation was seen as a sharp rebuke to the Republican president.
The Times said Republican senators Tom Cotton and Lindsey Graham and former Republican Senator Jim Talent had also been mentioned as possible replacements for Mr Mattis.