A Kurdish political body said Turkish forces and aligned rebels were shelling a village near Ras al-Ain, killing at least five members of the Kurdish-led Syrian Democratic Forces (SDF), despite the ceasefire pact.
The self-styled Syrian Democratic Council, the political wing of the SDF, called in an online statement for the dispatch of international observers to "preserve the temporary ceasefire and make it permanent."
US President Donald Trump spoke with Turkish President Recep Tayyip Erdogan about ceasefire violations.
"He told me there was minor sniper and mortar fire that was quickly eliminated," Trump tweeted. "He very much wants the ceasefire, or pause, to work."
Trump says the Kurds also want both a ceasefire and a more comprehensive solution and adds that there is "good will on both sides & a really good chance for success."
On Thursday, US Vice President Mike Pence said Turkey would pause its offensive for 120 hours to allow Syrian Kurdish fighters to withdraw from a "safe zone" sought by Ankara.
The Syrian Observatory for Human Rights, a war monitor, reported that at least 14 civilians were killed on Friday in Turkish airstrikes and shelling on rural Ras al-Ain.
At least eight SDF personnel were killed as result of the violence in the same area, according to the Britain-based watchdog.
However, Erdogan dismissed reports on clashes in north-eastern Syria as "speculation and misinformation."
"There is no such clash in question," he told reporters in Istanbul in his first public remarks after Thursday's deal with the US.
Erdogan claimed the Syrian Kurdish militia had already started to leave the area. Turkish security forces there "will not leave the area" as part of the deal, he added.
In Damascus, Syrian President Bashar al-Assad called for the withdrawal of all "illegal" foreign forces from the war-torn country.
"President al-Assad stressed that the current and future work should focus on stopping the [Turkish] offensive and the withdrawal of all Turkish, US and other illegal forces from all Syrian territories since they are occupation forces," Syria's state news agency SANA reported.
Al-Assad made the remarks at talks with Russia's presidential envoy for Syria, Alexander Lavrentiyev. Moscow is a key military ally of al-Assad.
US Secretary of State Mike Pompeo, who visited Turkey to help broker the ceasefire in north-eastern Syria, on Friday briefed NATO ambassadors on the deal in Brussels.
NATO Secretary General Jens Stoltenberg welcomed the ceasefire.
"I welcome that two NATO allies, the United States and Turkey, have agreed on a way forward," Stoltenberg said, adding: "We all know and understand that the situation in north-eastern Syria is fragile, difficult, but I believe that this statement can help to de-escalate the situation."
Pompeo played down reports of clashes since the ceasefire began around 24 hours ago.
"There was some activity today but we also saw some very positive activity," he said, noting that coordination measures were needed so Syrian Kurdish People's Protection Units (YPG) fighters could withdraw from the Turkish-controlled area.
"We are hopeful in the hours ahead that both the Turks, who were part of the agreement alongside of us, as well as the the YPG fighters in the region will take seriously the commitments that they made," Pompeo added.
Turkey had said its offensive, which started October 9 in north-eastern Syria, was aimed at Islamic State militants and the Syrian Kurdish People's Protection Units (YPG).
Turkey considers the YPG to be linked to the outlawed Kurdistan Workers' Party (PKK) waging an insurgency within the country. The US had relied on the YPG to help defeat Islamic State in Syria and is now being accused of abandoning the Syrian Kurds.
French President Emmanuel Macron said he has agreed with German Chancellor Angela Merkel and British Prime Minister Boris Johnson to hold a joint meeting with Erdogan in the coming weeks.
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