WASHINGTON, Dec. 20 (Xinhua) -- U.S. President Donald Trump said Thursday that Defense Secretary Jim Mattis is to retire at the end of February.

Mattis will "be retiring, with distinction," after having served the administration as the defense chief for the past two years, Trump tweeted.

"During Jim's tenure, tremendous progress has been made, especially with respect to the purchase of new fighting equipment," the president said.

He added that a new secretary of defense "will be named shortly."