Kurdish authorities in Syria's northern Afrin enclave have called on Syrian troops to defend the region's border, as a Turkish offensive continues there.
They said the "aim of this (Turkish) aggression is to cut more Syrian land by occupying Afrin".
Turkish-led forces began their assault in north-western Syria on Saturday.
Ankara regards Kurdish YPG fighters in Afrin as terrorists, and says they are linked to Kurdish PKK guerrillas who operate in Turkey itself.
Forty-eight Turkish-backed rebels and 42 YPG fighters have been killed in the fighting since Saturday, says the Syrian Observatory for Human Rights, a UK-based monitoring group.
In a separate development, Germany put plans on hold to upgrade German-made tanks used by Turkey amid a public outcry over the Turkish offensive.
What is the background to this?
This involves conflicting alliances and interests among regional and global powers.
Turkey accuses the YPG (People's Protection Units) of having links to the banned Kurdistan Workers' Party (PKK) group within its own borders.
"We call upon the Syrian state to carry out its sovereign duties towards Afrin and protect its borders with Turkey from attacks by the Turkish occupier," it added.
There has been no public response yet from the government in Damascus.
The YPG denies any direct organisational links to the PKK - an assertion backed by the US, which has provided the militia and allied Arab fighters with weapons and air support to help them battle Islamic State jihadists in Syria.
Tensions between the US and Turkey surfaced during an apparently confrontational phone call between Turkish President Recep Tayyip Erdogan and US President Donald Trump on Wednesday.
While a White House statement said Mr Trump had "urged Turkey to de-escalate" its Afrin operation, the Turkish foreign minister later insisted that Mr Erdogan had demanded US troops withdraw from northern Syria's Manbij region, which is also controlled by Kurdish forces.
Mr Erdogan has said the Turkish operation will be extended to Manbij - potentially bringing the Nato allies into direct conflict.
The White House statement says President Trump called on Turkey "to avoid any actions that might risk conflict between Turkish and American forces".
So far Turkish-backed forces seem to have made slow progress.