Turkey's President Erdoghan says Turkey may launch a new military operation in northern Syria at any moment after US had given a positive response to Turkey's plans.
Erdogan's remarks on Monday came days after he announced Turkish forces would launch a new cross-border operation against the US-backed Syrian Kurdish People's Protection Units (YPG) to the east of the Euphrates River in northern Syria.
The YPG is considered a terrorist organisation by Ankara.
American troops are also located to the east of the Euphrates River.
Erdogan spoke on the phone with Trump on Friday and they agreed to ensure "more effective coordination" between their countries' military operations in Syria.
"I spoke with Trump. The terrorists must leave the east of the Euphrates. If they don't go, we will remove them," Erdogan vowed during a televised speech in the central province of Konya.
Turkey views the YPG as an offshoot of the outlawed Kurdistan Workers' Party (PKK), which has battled against the Turkish state since 1984.
The PKK is blacklisted as a terrorist group by the US and European Union, while the YPG is not.
"They [YPG] are a source of discomfort with their terror corridor" along Turkey's border, Erdogan said.
Although Erdogan said Turkey could start an operation "at any moment", he appeared to indicate there was room for negotiation with the US.
"Since we are strategic partners with America, then we must do what is necessary," said Erdogan.
But he added the US "must fulfil promises" without giving further details.
US support for YPG
The YPG spearheaded Washington's fight against the Islamic State of Iraq and the Levant (ISIL) group in Syria under the banner of the Syrian Democratic Forces (SDF), which it leads.
However, American support for the armed group strained relations with Turkey.
Ankara has warned the US about observation posts Washington has been setting up in northern Syria to prevent any altercations between Turkish forces and the YPG.
Erdogan Turkey launched two military operations to help Syrian rebels recapture territory in Syria from ISIL and the YPG in August 2016 and January 2018.
The first offensive in northern Syria lasted until March 2017.
The second wrapped up in March 2018 after Ankara-backed rebels captured the YPG-held enclave of Afrin in northwestern Syria.
The National Liberation Front (NLF), made up of opposition groups in Syria's northwestern city of Idlib, said on Monday it would support the Turkish military operation.
"The [Syrian] regime has created a suitable environment for terrorist groups … to the detriment of the Syrian people," the NLF said in a statement.
"We will support any operation aimed at ensuring regional stability, ending the terrorist presence, and allowing the return of displaced persons to their homes.
We will not allow any group - be it the PKK/YPG or anyone else - to divide our country."
Syria's war has killed hundreds of thousands of people and displaced millions since starting in 2011 after the government's brutal repression of anti-government protests.
It has since spiralled into a complex conflict and proxy war involving many armed groups and world powers