Kurdish forces held out in a key border town Tuesday seven days into a deadly Turkish invasion of northeastern Syria that has caused mass displacement and reshaped the political map.
The United States slapped sanctions on its NATO ally in a bid to stop an assault that its own troop withdrawal from the area triggered but Ankara showed no sign of relenting.
Using a dense network of tunnels, berms and trenches, Kurdish fighters from the Syrian Democratic Forces (SDF) have been mounting a desperate defense of Ras al-Ain.
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.
Since launching their assault on October 9, Turkish-backed forces have secured more than 100 kilometres (60 miles) of border, but Ras al-Ain, which the Kurds call Siri Kani, has held out.
An AFP correspondent in the area said clashes around the town continued on Tuesday, despite repeated claims by Ankara in recent days that it had captured the area.
Further west, SDF fighters have been battling Turkey's Syrian proxies -- mostly former rebels paid and equipped by Ankara -- around the flashpoint town of Manbij.
US President Donald Trump announced a pullback from the border last week, a move which was widely interpreted as green-lighting a long-planned Turkish invasion.
Politically embattled at home, Turkish President Recep Tayyip Erdogan wants to create a 30 kilometre (20 mile) deep buffer zone on the Syrian side of the long border.
- Sanctions -
He wants to keep the SDF at bay -- Ankara considers them a terrorist group because of their links with the main Kurdish insurgency in Turkey -- and create a resettlement area for some of the 3.6 million Syrian refugees currently on Turkish soil.
The offensive has left dozens of civilians dead, mostly on the Kurdish side, and displaced at least 160,000 people.
Trump, who is campaigning for re-election but faces impeachment, is keen to deliver on a promise of pulling US troops out of the Syria quagmire.
More than 1,000 troops are now being withdrawn from northern Syria and the United States will keep only a residual contingent of some 150 troops in the south at the Al-Tanf base near the borders with Jordan and Iraq.
US Vice President Mike Pence said Monday he would travel to Turkey soon and added that Trump had asked Erdogan to stop the offensive.
In a bid to force Turkey's hand, Washington slapped sanctions on its defense, 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 the Islamic State group that cost the lives of 11,000 of their fighters, the Kurds turned to Damascus.
Syrian government forces rushed north on Monday as part of a Russian-brokered deal aimed at preventing Turkish-backed forces from moving any deeper into the country.
- Transfers to Iraq? -
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, only months after the demise of its so-called "caliphate".
It would also increase the risk that some of them might find their way back to Europe to plan and conduct high-profile terror attacks.
"The United States' decision to withdraw from Syria has emboldened jihadists worldwide. The return of the Islamic State is now a given," the Institute for the Study of War said in a brief.
The SDF have warned that their fighters were mobilized 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.