French president Emmanuel Macron yesterday blasted Donald Trump's decision to withdraw US troops from Syria.

Mr Macron said during a visit to Chad: 'I very deeply regret the decision made on Syria.

'To be allies is to fight shoulder to shoulder. It's the most important thing for a head of state and head of the military. An ally should be dependable.

Emmanuel Macron (pictured on Sunday in N'Djamena, Chad) said he 'deeply regrets' Donald Trump's decision to withdraw 2,000 troops from Syria

'An ally must be reliable, to coordinate with its other allies.'

His comments came as the US envoy in the global fight against Islamic State followed Mr Trump's defence secretary Jim Mattis out of the White House door in protest at the President's policies.

Brett McGurk quit over the 'reckless' plan to pull 2,000 troops out of Syria with the President claiming the terrorists had been defeated in their homeland.

Mr McGurk said the IS militants were on the run, but not yet defeated.

Macron paid tribute to Defense Secretary James Mattis, who said he was resigning on Thursday following Trump's Syria announcement.

'I want here to pay tribute to General Mattis... for a year we have seen how he was a reliable partner,' Macron said at a news conference with his Chadian counterpart Idriss Deby.

It comes as US defence secretary Jim Mattis (pictured left with Trump) resigned over the decision

Mattis, 68, was one of Trump's first cabinet picks and has spent nearly two years at the Pentagon.

In his resignation letter Mattis spelled out to the world what seemed obvious to many observers: Trump's world view was irreconcilable with his own.

'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' immersion in these issues,' Mattis wrote to Trump, who has sought closer ties with Russia and heaped contempt on NATO and other alliances.

'Because you have the right to have a Secretary of Defense whose views are better aligned with yours on these and other subjects, I believe it is right for me to step down from my position.'