Donald Trump suggested Monday that Syria's formerly US-allied Kurds could look to 19th century French emperor Napoleon Bonaparte for protection after the US president ordered the departure of nearly 1,000 US troops from the country.

Turkey was threatening to invade northeastern Syria after launching a military assault on the Kurds last week, leaving more than 300 dead on both sides and sending 160,000 refugees fleeing.

"Anyone who wants to assist Syria in protecting the Kurds is good with me, whether it is Russia, China, or Napoleon Bonaparte. I hope they all do great, we are 7,000 miles away!" Trump wrote on Twitter.

He defended his weekend order to vacate northeastern Syria and abandon the Kurds, saying that the US mission to defeat Islamic State in the region had been achieved "100 percent."

The president said Syrian President Bashar al-Assad should defend the region.

"Let Syria and Assad protect the Kurds and fight Turkey for their own land. I said to my Generals, why should we be fighting for Syria and Assad to protect the land of our enemy?" Trump wrote.