Trump vows allies will not 'take advantage' after Mattis exit

Brett McGurk, the U.S. special envoy to the anti-Islamic State group coalition, has resigned, a State Department official said Saturday, capping a chaotic week that saw the departure of Defense Secretary Jim Mattis and Donald Trump's stunning decision to pull troops from Syria.

A fracture developed last week over Trump's decision to withdraw USA troops from Syria and worsened after Mattis' public disagreement with Trump, aired in his resignation letter. "The secretary of defence serves at the pleasure of the president", the statement read.

Yuri Gripas/ReutersDefense Secretary James Mattis.

The withdrawal will see some 2,000 U.S. troops removed from Syria, a plan announced last week.

Mr Trump made his displeasure with Mr Mattis clear on Saturday night by tweeting that he had been "ingloriously fired" by former President Barack Obama and he had given Mattis a second chance.

A senior administration official told Reuters that Shanahan "has a deep-seated understanding of military operations, and global security affairs, and importantly, has the breadth of large-scale business management experience that will enable him to effectively oversee the Defense Department".

Officials have told Fox News the US has no plans to withdraw the more than 5,000 American troops in neighboring Iraq.

But Trump's announcement appeared to forestall that trip.

Asked whether Trump wanted a Pentagon leader willing to challenge him or someone in lock step with his views, Mulvaney said "a little bit of both".

"I call on everyone... not to forget what we owe them", he said.

On Sunday, Trump announced that Mattis would be leaving the Pentagon on January 1, two months earlier than planned. Mattis had been at work on Friday, and defense officials had insisted he was planning to stay through February, when he would attend a North Atlantic Treaty Organisation defense ministers meeting.

Mattis, whose embrace of North Atlantic Treaty Organisation and America's traditional alliances often put him at odds with Trump, had advised against the Syria withdrawal - one of the factors in his resignation.

Trump also tweeted on Monday that Saudi Arabia had agreed "to spend the necessary money needed to help rebuild Syria, instead of the United States". Whatever Trump might have tweeted or uttered during summits, Mattis' stewardship of the massive USA defense bureaucracy would result in predictability. Lindsey Graham, R-South Carolina, said it was "a sign of American weakness". "But keep in mind it's not unusual for a president to lose members of the Cabinet over these types of disagreements".

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 U.S. and played a major role in the war against Islamic State (IS) militants, but are deemed terrorists by Ankara. "After many years they are coming home".