Secretary of State Mike Pompeo, not the president, notified Mattis of the decision, said a senior administration official who insisted on anonymity to discuss personnel issues.
Shanahan, a longtime Boeing Co. executive, was nominated for the deputy job in early 2017. Mr. Trump, however, said Sunday that the Pentagon chief would depart by January 1 and be replaced by his deputy and longtime Boeing executive, Patrick Shanahan.
It is unusual for the Pentagon to have an acting secretary of defense.
Mr Trump's sudden decision also sparked turmoil within his administration, prompting the resignation of Mr Brett McGurk, the special envoy to the anti-ISIS coalition.
"With me, hit hard instead by the Fake News Media".
Christmas opening times for Tesco, Sainsbury’s, Lidl and Aldi 2018
Oriental Jade is open until 9:30 p.m. on Christmas Eve , and will have a special buffet from noon to 8 p.m. on Christmas Day . Calgary Transit will operate on a Sunday level of service for trains and buses on Christmas Eve and Boxing Day .
The order has been signed for the withdrawal of American troops from Syria, where they have been deployed to assist in the war against the Islamic State jihadist group, a USA military spokesperson has said.
Jim Mattis served for 44 years in the Marine Corps before retiring as a general in 2013.
Names that are quietly beginning to surface include some of the civilian leaders of the military services such as Air Force Secretary Heather Wilson and Army Secretary Mark Esper, an acknowledgement that someone who has already undergone Senate confirmation is considered a safer bet.
The White House's abrupt decision to order the full departure of USA ground forces in Syria on Wednesday provoked a flurry of criticism from Republicans and Democrats. Sen. "It is the very definition of patriotism and integrity", Tom Mattis, James Mattis's older brother, told The Seattle Times earlier this week.
The sudden change stripped Mattis of any chance to further frame national security policy or smooth rattled relations with allies over the next two months.
Japan restarting commercial whaling, ignoring global moratorium
Fisheries officials say that whale meat is more popular with older segments of the Japanese population than among the young. Activist groups slammed the decision, with Greenpeace calling it a " sneaky " announcement.
Trump and Turkish President Recep Tayyip Erdogan spoke by telephone on Sunday and "agreed to ensure coordination between their countries' military, diplomatic and other officials to avoid a power vacuum which could result following any abuse of the withdrawal and transition phase in Syria", Erdogan said in a statement.
Turkey was a rare ally that lauded Trump's decision on Syria, a country where it will now have a freer rein to target Kurdish fighters who were armed and trained by the USA and played a major role in the war against Islamic State (IS) militants, but are deemed terrorists by Ankara.
Bernstein concluded: "They're talking to each other, there is coming to be a much greater consensus that he is unfit to be the president of the United States".
Donald Trump Says US Pullout From Syria Justified, 'Erdogan Will Eradicate ISIS'
He noted that Ankara does not trust Washington, which supports the Kurdish forces in Syria along the Turkish southern border. We discussed ISIS , our mutual involvement in Syria, & the slow & highly coordinated pullout of USA troops from the area.