Emmanuel Macron, France's president, speaks ahead of the Balkan summit at the Chancellery in Berlin, Germany, on Monday, April 29, 2019.

French President Emmanuel Macron, in an interview with British weekly The Economist, warned fellow European countries that they could no longer rely on the United States to defend North Atlantic Treaty Organization (NATO) allies.

"What we are currently experiencing is the brain death of NATO," Macron was quoted as saying.

Asked whether he still believed in the Article Five "collective defense" stipulations of NATO's founding treaty - under which an attack against one ally is considered as an attack against all allies - Macron answered: "I don't know."

"(NATO) only works if the guarantor of last resort functions as such. I'd argue that we should reassess the reality of what NATO is in the light of the commitment of the United States," Macron added.

The United States is showing signs of "turning its back on us", as demonstrated by President Donald Trump's sudden decision last month to pull troops out of northeastern Syria last month without consulting the allies, the French leader said.

That move caught NATO's leading European powers - France, Britain and Germany - by surprise and paved the way for Turkey, another NATO member, to launch a cross-border military operation targeting Syrian Kurdish forces.