Turkey will destroy a "terror corridor" along its border in northern Syria regardless of any deal reached with the United States to create a safe zone in the Kurdish-controlled area, President Recep Tayyip Erdogan said.
Turkish and US officials are discussing the creation of the safe zone east of the Euphrates river to address Turkey's concerns about the presence of US-backed Syrian Kurdish fighters. Turkey considers the Kurdish YPG militia, who comprised the bulk of a Syrian force that defeated ISIS in north-eastern Syria with US support, as terrorists with links to a Kurdish insurgency in Turkey.
“We are determined to shatter the terror corridor east of the Euphrates, no matter how the negotiations with the US to establish a safe zone along the Syrian borders concludes,” Mr Erdogan told members of his AK Party at a meeting on Friday.
"Those who engage in bullying by putting their trust in foreign forces will tomorrow find themselves in the grave," the president said, in an apparent reference to the YPG.
The head of the US military Central Command, General Kenneth McKenzie, visited Syria's Kurdish-held areas on Monday for the first time since he took his post in March and met the Kurdish commander of the US-backed Syrian Democratic Forces, Gen Mazlum Abdi, in the border town of Kobane.
According to an SDF spokesman, they discussed the proposed safe zone as well as further co-operation with the international coalition against ISIS to prevent a resurgence of the extremist group.
At the same time, the US Special Envoy to Syria James Jeffrey was holding talks Turkish Defence Minister Hulusi Akar and other top officials in Ankara.
The Turkish defence ministry said military officials from both countries had started work to "establish a planned safe zone in northern Syria in a co-ordinated way".
Turkey has recently stepped up warnings that it could send troops into Syria to drive back the Kurdish fighters if talks with the US drag on, and has been sending reinforcements to its border area.
Since 2016, Turkey has launched two cross-border offensives into Syria, the first against ISIS and the second against Kurdish fighters west of the Euphrates.
Mr Erdogan said a new Turkish incursion into Syria east of the Euphrates would cut off contact between Syria's Kurdish fighters and those in neighbouring Iraq, where Turkey has been carrying out air strikes targeting alleged hideouts of the Kurdistan Workers' Party (PKK), the Kurdish group waging an insurgency in Turkey.
Meanwhile, the Syria foreign ministry rejected any agreement reached between the US and Turkey on northern Syria as an infringement of its sovereignty.
"The pretexts of national security the Turkish regime is putting forward belie its policies and behaviours as a main base for terrorism, offering it all kinds of military and logistical support," a ministry statement said.
Kurdish-controlled north-east Syria and the opposition-held Idlib region in the north-west are the two main pockets of territory that remain outside of Syrian government control after eight years of civil war.
Turkey has backed rebel groups fighting the regime of Syrian President Bashar Al Assad, who has managed to hold on to power with the help of Iran and Russia.