File photo shows the U.S. Defense Secretary James Mattis at the Pentagon, Virginia, the United States, on Aug. 7, 2018. (Xinhua/Liu Jie)

WASHINGTON, Dec. 23 (Xinhua) -- U.S. President Donald Trump announced Sunday that he has picked Deputy Secretary of Defense Patrick Shanahan as the acting Pentagon chief.

Shanahan will assume the role starting Jan. 1, 2019, Trump said in a tweet Sunday noon.

"Patrick has a long list of accomplishments while serving as Deputy, & previously Boeing. He will be great!" The president added.

The announcement came after Trump said earlier in the past week that current defense secretary James Mattis will "retire" at the end of February next year.

Trump was reportedly furious at days of negative news coverage over Mattis' resignation and his rebuke over the administration's treatment of U.S. allies.

"One core belief I have always held is that our strength as a nation is inextricably linked to the strength of our unique and comprehensive system of alliances and partnerships," Mattis wrote in a resignation letter.

He added that his views on treating the allies with respect are strongly held and informed by over four decades of immersion in these issues.

Trump said when announcing Mattis' departure that the 68-year-old former Marine Corps general would "be retiring, with distinction."

Shanahan became deputy secretary of defense on July 2017. Before that, he served as Boeing senior vice president, Supply Chain & Operations.