In his strongest warning yet, the Turkish president threatened on Saturday to launch a military operation into northeastern Syria, where US troops are deployed and have been trying to defuse tensions between Washington's two allies - Turkey and the Syrian Kurds.
Recep Tayyip Erdogan's threats were a warning that a US-Turkish deal to secure Syria's troubled border with Turkey was faltering. He said a Turkish military operation against the US-backed Kurdish forces could begin "maybe today, maybe tomorrow".
The Turkish military has been dispatching units and defense equipment to southeastern Sanliurfa province in the past month. Mr Erdogan had expressed frustration, threatening a unilateral operation, but this was his most specific threat amid concerns from the Syrian Kurds of a limited military operation.
"We have given all kinds of warning regarding the (area) east of the Euphrates to the relevant parties. We have acted with enough patience," Mr Erdogan said.
A Turkish military operation, however limited, would put major pressure on the more 1,000 US troops in northeastern Syria and who operate closely with the Kurdish-led forces, whether to implement the security mechanism or in fighting IS.
The Turkish leader has repeatedly expressed frustration with Washington's support for Kurdish groups in Syria. His threats continued despite a deal reached with Washington in August to carry out joint patrols and move Syrian Kurdish fighters away from the border.
The Kurdish-led Syrian Democratic Forces said it is committed to the agreement between Turkey and the U.S. to preserve stability in the region.
"However, we will not hesitate to turn any unprovoked attack by Turkey into an all-out war on the entire border to DEFEND ourselves and our people," SDF spokesman Mustafa Bali tweeted Saturday.
Turkey views the People's Protection Units, or YPG, as an extension of the Kurdistan Workers' Party, or PKK, which has waged an insurgency against Turkey for 35 years.
Turkey and the US disagree on the size of the area to be monitored by joint patrols, and also on who is to oversee it. Turkey wants its soldiers to monitor an area as deep as 19 miles. The US and the Kurdish forces have identified an area only as deep as 9 miles deep.
Mr Erdogan has said the joint patrols with the US are not enough and appear to be designed to waste time. He called the joint ground and air patrols a "tale".
Mr Erdogan said his country wants to send 2 million Syrian refugees now in Turkey to the area it has called a "safe zone". But the Syrian Kurdish group administering the area said only those from the area can return - a number likely to be much smaller.
Mr Erdogan also demanded an answer from the US on whether it will consider the Syrian Kurdish fighters "terrorists".