United States, Department of Defence, Chief of Staff, Rear Admiral Kevin Sweeney has resigned, a month after Defence Secretary James Mattis announced his departure.
Rear Admiral Sweeney said in a statement that the time is right to return to the private sector.
He is now the third senior Pentagon official to announce his resignation since President Donald Trump announced US forces would leave Syria.
Officials said, there is no timetable for the troop departure.
On Tuesday, Secretary of State Mike Pompeo will embark on a week-long tour of West Asia designed to reassure allies in the region.