The United States slapped sanctions on its Nato ally in a bid to stop an assault that its own troop withdrawal triggered, but Ankara showed no sign of relenting
Kurdish fighters put up fierce resistance on Tuesday to Turkish forces battling to seize a key town in northeastern Syria, as the violence forced international aid organizations to halt their activities.
The United States slapped sanctions on its Nato ally in a bid to stop an assault that its own troop withdrawal triggered, but Ankara showed no sign of relenting.
Syria's regime dispatched more troops to the northeast to contain Ankara's advance - their most significant deployment in the Kurdish-controlled region since they started withdrawing from the area in 2012.
It follows a deal clinched Sunday between Damascus and the Kurds that saw government troops raise the Syrian flag in the flashpoint northern city of Manbij on Tuesday, after US forces pulled out.
Regime troops had entered the city near the border on Monday night, as pro-Turkey fighters massed to the west ahead of a planned assault.
Kurdish combatants from the Syrian Democratic Forces (SDF) are battling Turkish forces and their Syrian proxies - mostly former rebels paid and equipped by Ankara - in various parts of the northeast.
East of Manbij, the Kurds are mounting a desperate defence in the border town of Ras al-Ain, using a dense network of tunnels, berms and trenches.
They launched "a large counterattack against Turkish forces and their Syrian proxies near Ras al-Ain," the Britain-based Syrian Observatory for Human Rights said.
Transfers to Iraq?
In a bid to force Turkey's hand, Washington slapped sanctions on its defence, interior and energy ministers, freezing their US assets and making US transactions with them a crime.
"I am fully prepared to swiftly destroy Turkey's economy if Turkish leaders continue down this dangerous and destructive path," said Trump, who until recently had touted his friendship with Erdogan.
Abandoned by the US, their chief ally in years of battles against IS that cost the lives of 11,000 of their fighters, the Kurds turned to Damascus.
European governments in particular are worried that the chaos in the area could lead to mass breakouts by thousands of IS fighters detained by Kurdish forces.
They have warned this would lead to a resurgence of the jihadist organisation and increase the risk that some of them might return to Europe to plan and conduct terror attacks.
The SDF have warned that their fighters were mobilised to defend against the Turkish advance and not available to fully guard IS prisoners.
That has already resulted in the escape of hundreds of foreign fighters' relatives, although Trump suggested the SDF may have deliberately let them go to gain leverage.
Human Rights Watch warned European countries against attempts to have their detained nationals transferred en masse to Iraq for prosecution.
The watchdog warned it would be illegal for these countries to send nationals to stand trial in a country where they risk execution and where due process is consistently violated.
A European diplomatic source said France was discussing a transfer with Iraqi officials on Tuesday.