Washington

US President Donald Trump on Sunday said he was replacing Defence Secretary Jim Mattis two months earlier than had been expected, a move officials said was driven by Mr Trump's anger at Mr Mattis' resignation letter and its rebuke of his foreign policy.

On Thursday, Mr Mattis abruptly said he was quitting, effective Feb 28, after falling out with the president over his foreign policy, including surprise decisions to withdraw all troops from Syria and start planning a drawdown in Afghanistan.

Mr Trump has come under withering criticism from fellow Republicans, Democrats and international allies over his decisions about Syria and Afghanistan, against the advice of his top aides and US commanders.

The exit of Mr Mattis, highly regarded by Republicans and Democrats alike, added to concerns over what many see as Mr Trump's unpredictable, go-it-alone approach to global security. Mr Trump said Deputy Defence Secretary Patrick Shanahan would take over on an acting basis from Jan 1.

In announcing his resignation, Mr Mattis distributed a candid resignation letter addressed to Mr Trump that laid bare the growing divide between them, and implicitly criticised the president for failing to value America's closest allies, who fought alongside the United States in both conflicts. Mr Mattis said Mr Trump deserved to have a defence secretary more aligned with his views.

Mr Trump, who tweeted on Thursday that Mr Mattis was "retiring, with distinction, at the end of February", made his displeasure clear on Saturday by tweeting that the retired Marine general had been "ingloriously fired" by former president Barack Obama and he had given Mr Mattis a second chance.

Mr Obama removed Mr Mattis as head of US Central Command in 2013 because of what officials at the time said were perceived to be his hawkish views on Iran.

Thursday's tweet was dictated to an aide to send before Mr Trump read Mr Mattis' resignation letter, a senior administration official told reporters on Sunday. "That's not the kind of letter of resignation I think you should write," the official said, adding Secretary of State Mike Pompeo had told Mr Mattis on Sunday he would be leaving on Jan 1.

In a tweet on Sunday, Mr Trump praised Mr Shanahan, a former Boeing Co executive, as "very talented". In his letter, Mr Mattis had said he would step down at the end of February to allow for a successor to be confirmed and attend Congressional hearings and a key Nato meeting.

A senior White House official said that Mr Trump was irked by the attention given to Mr Mattis' resignation letter. "He just wants a smooth, more quick transition and felt that dragging it out for a couple of months is not good," the official said, on condition of anonymity. The official said Mr Trump was expected to pick a nominee for defence secretary over the next couple of weeks.

Defense Department spokeswoman Dana White said Mr Mattis would work with Mr Shanahan and Pentagon leadership to ensure the department "remains focused on the defence of the nation during this transition".

Mr Shanahan, in his job as deputy defence secretary, has largely focused on internal Pentagon reform and issues like the creation of a Space Force, a project championed by Mr Trump but resisted by some lawmakers and some in the Pentagon.

A senior administration official told Reuters that Mr 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".

In a shock announcement on Wednesday, Mr Trump said he was withdrawing US troops from Syria, citing its cost both in terms of lives of US soldiers and financially. A day later, US officials said the United States was planning on pulling out about half of the 14,000 US troops in Afghanistan.

Mr Mattis, whose embrace of Nato and America's traditional alliances often puts him at odds with Mr Trump, had advised against the Syria withdrawal - one of the factors in his resignation.

On Sunday, Mr Trump said in a tweet that he had spoken with Turkish President Tayyip Erdogan about a "slow and highly coordinated" withdrawal, suggesting that he might slow down the process after the barrage of criticism.

A US military official, speaking on condition of anonymity, said the withdrawal would be "safe, professional and deliberate" but was not aware of any new guidance from the White House. A plan on the pull-out is expected to be presented by commanders to the Pentagon this week, the official said. REUTERS