Smoke rises from Syrian city of Ras al Ayn following an attack from Turkey (Picture: PA).
Donald Trump says the crisis which has followed the withdrawal of US troops from Syria is not America's fight.
Turkey launched a military operation against Kurdish fighters on Wednesday 9 October.
The predominantly Kurdish Syrian Democratic Force fought alongside American soldiers in Syria against so-called Islamic State.
The US President's decision to withdraw was strongly condemned in the US - including by usual Republican allies in Congress and analysts - as destabilising the region and abandoning a Kurdish ally.
Critics say the pull out has allowed Turkey to invade the north-east, where it has been attacking Kurdish fighters whom Turkey views as terrorists.
Mr Trump said Syria was getting "some help with Russia and that's fine".
"If Russia wants to get involved with Syria, that's really up to them," he said.
"It's not our border. We shouldn't be losing lives over it."
The President says the approximately 1,000 troops are "largely out", but a US official says they have not yet begun flying out of Syria in significant numbers.
Military equipment is being gathered and flown out, the official said.
"It's not between Turkey and the United States, like a lot of stupid people would like you to believe," Mr Trump said.
"They've got a lot of sand over there," he said. "So there's a lot of sand that they can play with."
"Syria's friendly with the Kurds. The Kurds are very well protected. Plus, they know how to fight. And, by the way, they're no angels."
Mr Trump imposed new sanctions on Turkey this week in an attempt to force President Recep Tayyip Erdogan to end his assault.
Mr Trump is also sending a delegation led by vice president Mike Pence to Turkey to meet with Mr Erdogan in an attempt to help negotiate a cease-fire.