Photo released by Turkish Defense Ministry shows Turkish army launches a military operation into northern Syria on the Turkey-Syria border, on October 9, 2019. Photo:Xinhua

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 US 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 kilometers of border, but Ras al-Ain, which the Kurds call Siri Kani, has held out.

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-kilometer-deep buffer zone on the Syrian side of the long border.

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.

China on Tuesday urged Turkey to "stop its military operations and return to the right way to find a political solution to the problem."

"China has always opposed the use of force in international relations and holds that all parties should earnestly abide by the purposes and principles of the Charter of the UN and resolve the issue through political and diplomatic channels within the framework of international law," Chinese Foreign Ministry spokesperson Geng Shuang said Tuesday at a daily press briefing.

"Syria's sovereignty, independence, unity and territorial integrity should be respected and safeguarded," Geng added. 

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 organization, only months after the demise of its so-called caliphate.

"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.

Beijing also voiced its concerns about Syria's counter-terrorism situation.

The counter-terrorism situation in Syria remains grim, and the relevant military actions may lead to the spread of terrorists. We urge Turkey to shoulder its responsibility and work with the international community to combat terrorism, Geng said.