0203 GMT July 20, 2019
Trump steadfastly defended his sudden push for retrenchment, vowing that the United States would no longer be the "policeman of the Middle East" and saying the 2,000-strong US force in Syria was no longer needed as the Daesh group had been defeated, AFP reported.
Mattis, a battle-hardened retired four-star general seen as a moderating force on the often impulsive president, made little attempt to hide his disagreements with Trump.
"Because you have the right to have a secretary of defense whose views are better aligned with yours," Mattis said in a letter to Trump, "I believe it is right for me to step down from my position."
"My views on treating allies with respect and also being clear-eyed about both malign actors and strategic competitors are strongly held and informed by over four decades of immersion in these issues," Mattis wrote.
One day after the surprise announcement on Syria, a US official said that Trump had also decided on a "significant withdrawal" in a much larger US operation – Afghanistan.
Some 14,000 troops are fighting the Taliban in Afghanistan as part of the longest-ever US war, launched in response to the September 11, 2001 attacks. The Wall Street Journal reported that more than half would be returning.
No impact on security
A spokesman for President Ashraf Ghani said on Friday that a significant reduction in the number of US troops in Afghanistan won't impact upon the security of the war-torn country.
"If they withdraw from Afghanistan it will not have a security impact because in the last 4 1/2 years the Afghans have been in full control," Ghani's spokesman, Haroon Chakhansuri, said via social media.
On Twitter Thursday, Trump had only praise for his defense secretary, who will serve until the end of February, crediting him with achieving "tremendous progress."
US lawmakers across the political spectrum voiced concern over a rebirth of the Daesh terrorist group in Syria and sounded an alarm as Mattis unmoors from the unpredictable administration.
Some of the countries welcomed the US decision while the US allies expressed concern over the Washington’s decision.
Russia, Turkey welcomes US decision
"The fact that the US has decided to withdraw its troops is right," President Vladimir Putin said during an annual year-end press conference, saying that "on the whole I agree with the US president" on the level of damage inflicted on the Daesh.
Turkish President Tayyip Erdogan said on Friday that Turkey would postpone a military operation against Syrian Kurdish fighters in northeast Syria as he “cautiously” welcomed Washington’s decision to withdraw its troops in the area.
Erdogan has long castigated his NATO ally over northeastern Syria, where Washington has backed Syrian Kurdish YPG fighters.
Turkey considers the YPG a terrorist organization and an offshoot of the armed Kurdistan Workers’ Party (PKK).
Erdogan announced plans last week to start an operation east of the Euphrates River in northern Syria to push the YPG out of the area, which it largely controls.
US allies express concern
Key allies of Washington expressed concern on Friday about the resignation of Mattis and the policies of Trump that prompted it, praising Mattis as a committed partner, Reuters reported.
“Secretary Mattis has made a key contribution to keeping NATO strong and ready to deal with the significant security challenges we face,” NATO spokeswoman Oana Lungescu said. “He is widely respected as a soldier and a diplomat.”
Mattis has been seen in Europe as firmly committed to the North Atlantic Treaty Organization (NATO) military alliance, unlike his ex-boss.
Trump has warned European allies the United States could withdraw its support unless they boost defense spending.
“We are grateful for the iron-clad commitment of the United States to NATO. US leadership keeps our transatlantic alliance strong,” Lungescu said.
Former Belgian Prime Minister Guy Verhofstadt, head of the liberals in the European Parliament, said the resignation only made it more urgent for the European Union to push on with its plans to bolster its own defense capabilities.
Mattis’ resignation also sparked concern among Washington’s Asia-Pacific allies, who credit the retired general with building trust and tempering isolationist impulses.
After being tipped off by White House sources and diplomats, French President Emmanuel Macron called Trump on Tuesday to warn him against the Syria decision, a French official said.
“He told him: Be careful, we think that would be a bit too early’,” the official said.
German Defense Minister Ursula Von der Leyen called for clarity on future policies.
“Because the United States has such a prominent role and responsibility in the global security architecture, it is important for everyone to quickly get clarity about succession and the future course,” she said in a statement.