Breaking: Trump announces retirement of Defense Secretary James Mattis

President Donald Trump tweeted Thursday that General James Mattis was retiring as his Secretary of Defense and will be replaced soon.

"General Jim Mattis will be retiring," the president tweeted, "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," he added in another tweet. "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," he concluded. "I greatly thank Jim for his service!"

The announcement came just a day after the stunning report that the president was planning to pull U.S. troops out of Syria, and another report Thursday that he was considering doing the same in Afghanistan.

Mattis released a letter explaining that part of the reason he was resigning was the difference in his policy positions from those of the president. The letter, in contrast to the president's tweets, appears to claim that Mattis resigned, not that he retired.

"Because you have the right to have a Secretary of Defense whose views are better aligned with yours on these and other subjects," Mattis said in the letter, "I believe it is right for me to step down from my position."

He also highlighted the authoritarian schemes of Russia and Chinas opposed to America's interests.

"I believe we must be resolute and unambiguous in our approach to those countries whose strategy interests are increasingly in tension with ours," he added. "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 promise their own interests at the expense of their neighbors, America and our allies."

He said he will stay in the position until February 28.

Here's CNBC's report on the sudden announcement: