The US Defense Secretary James Mattis on Thursday announced that he would resign from his position at the end of February after disagreeing with US President Donald Trump over his approach to policy in the Middle East.

Mattis reportedly opposed Trump’s plans to pull troops out of Syria.

“General Jim Mattis will be retiring, with distinction, at the end of February, after having served my Administration as Secretary of Defense for the past two years. During Jim’s tenure, tremendous progress has been made, especially with respect to the purchase of new fighting equipment. General Mattis was a great help to me in getting allies and other countries to pay their share of military obligations. A new Secretary of Defense will be named shortly. I greatly thank Jim for his service!,” Trump said in a tweet on Thursday. 

“Because you have the right to have a Secretary of Defense whose views are better aligned with yours and other subjects, I believe it is right for me to step down from my position,” Mattis wrote.

He said that his end date would be on February 28.

“My views on treating allies with respect and also being clear-eyed about both malign actors and strategic competitors are strongly held and informed by over four decades of immersion in these issues,” Mattis wrote. “We must do everything possible to advance an international order that is most conducive to our security, prosperity and values, and we are strengthened in this effort by the solidarity of our alliances.”

Trump’s announcement that US troops in Syria would be withdrawn, while declaring that ISIS has been defeated, drew criticism from lawmakers in both parties on Capitol Hill, and reportedly came as a surprise to White House staff. The US media reported that Trump also is considering withdrawing troops from Afghanistan.

Mattis also suggested that he disagreed with Trump on how the president has dealt with Russia and China. 

Mattis wrote that “I believe that we must be resolute and unambiguous in our approach to those countries whose strategic interests are increasingly in tension with ours. It is clear that China and Russia, for example, want to shape a world consistent with their authoritarian model — gaining veto authority over other nations’ economic, diplomatic and security decisions — to promote their own interests at the expense of their neighbors, America and our allies.”