Defense Secretary James Mattis announced on Thursday he would be resigning from his position in the Trump administration -- leaving his role at the end of February.
The news came a day after President Donald Trump's surprise plans to withdraw American troops from Syria became public.
Mattis' resignation letter amounts to a rebuke of several of Trump's foreign policy views, with the outgoing defense secretary touting the importance of US alliances and of being "unambiguous" in approaching adversaries like Russia and China.
It is devoid of any praise for the President.
In his letter of resignation, Mattis said, "Because you have the right to have a Secretary of Defense whose views are better aligned with yours on these and other subjects, I believe it is right for me to step down from my position."
Read his full letter of resignation here.