Department of Defence chief of staff Kevin Sweeney has resigned, weeks after the Defence Secretary James Mattis announced his departure.

Sweeney said in a statement “after two years in the Pentagon, I decided it was time to go back to the private sector, it was an honor to serve again with men and women of the Ministry of Defense.

Mattis, who served two years as defense minister, originally planned to resign in February, but Trump chose to replace him sooner after he wrote a terse letter of resignation over his differences with the US president.

Sweeney’s decision is the latest in a series of resignations by senior Pentagon officials. Last week.

According to a senior Pentagon official under former President Barack Obama, “in normal circumstances, the resignation of the chief of staff after the departure of the Secretary of Defense is not only normal, but expected. But these are not normal circumstances. With so many leadership gaps in the Pentagon and the uncertainty about future leadership, Sweeney’s departure will add to the growing sense of instability in an institution whose prosperity is precarious.“