Turkey and the US reached a deal for northern Syria on Wednesday to establish joint operations centre.
A joint statement by the Turkish Ministry of Defence and the US embassy in Ankara said the two sides agreed to set up the Turkey-based operations centre "as soon as possible" and that the safe zone "would become a "peace corridor", without providing further details.
"Syria expresses categorical rejection of the agreement announced by the US and Turkish occupations on establishing the so-called [safe zone] which constitutes a blatant aggression against the sovereignty and territorial integrity of the Syrian Arab Republic and a flagrant violation of the principles of the international law and the UN Charter," a Syrian source at the Ministry of Foreign Affairs told SANA press agency on Thursday.
"This agreement has very clearly exposed the US-Turkish partnership in the aggression against Syria which serves the interest of the Israeli occupation entity and the Turkish expansionist ambitions and it unequivocally exposed the misleading and evasiveness which govern the policies of the Turkish regime," the statement continued.
The US-Turkey statement did not specify how and when the zone would be created, but it appeared to avert a threatened Turkish operation into the region east of the Euphrates River in Syria.
"Syria calls on the international community and the UN to condemn the US-Turkish flagrant aggression which constitutes a dangerous escalation and poses a threat to peace and security in the region and the world and hinders all positive efforts for finding a solution to the crisis in Syria," the government statement concluded.
Northeastern Syria is currently under the control of the US-backed Kurdish-led Syrian Democratic Forces (SDF), largely comprising of the People's Protection Units (YPG).
Turkey deems the YPG to be an extension of the outlawed Kurdistan Workers' Party (PKK), which launched an armed campaign against the state 35 years ago.
Turkey has for weeks been pressing to establish a 30-40km deep zone within Syria, seeking the removal of the YPG from the area and the destruction of their tunnels and fortifications.
The US, on the other hand, has tried to limit the safe zone to 10km.
On Tuesday, Turkey's President Recep Tayyip Erdogan warned the country was running out of patience with regards to a Turkey-US deal.
"Turkey has the right to eliminate all threats against its national security," he said in a televised speech. "God willing, we will carry the process started with [previous offensives into Syria] to the next stage very soon."
Following that speech, the US defence secretary, Mark Esper, said that any unilateral action by Turkey would be "unacceptable".
Turkey and the US are NATO allies but have grown increasingly estranged over a number of issues, including American support for the Kurds and Turkey's decision to buy a Russian S-400 missile defence system. Turkish media outlets have often shown images in recent weeks of military convoys heading for the border area, carrying equipment and fighting units. Turkey has twice carried out unilateral offensives into northern Syria against ISIL and YPG, in 2016 and 2018 respectively.
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