A shopkeeper in Raqqa, who asked not to be named out of fear for his safety, said by text message that a large number of Arab fighters in the Syrian Democratic Forces were being sent from Raqqa to Manbij to prepare for a Turkish attack.
Overnight airstrikes were also launched against US-backed Kurdish forces in the area with Turkish politicians telling reporters they meant to clear the area of all those they consider terrorists in a swift operation.
It said militia targets were also being destroyed by Turkish warplanes and multiple rocket launchers. Turkish officials said that only one Syrian had refugee died and that 37 people were wounded.
The land operation by Turkish forces, which began Sunday morning, comes as Turkey intensified air and artillery strikes on the Syrian-Kurdish enclave, Afrin, over the weekend.
He told a news outlet that the Syrian government was informed of the operation in advance, but the Syrian government, speaking through the state-run news agency SANA, said it wasn't notified.
It considers them a terrorist group.
He believes that they are an armed wing of the Kurdistan Party (PKK), which since 1984 has been fighting for the creation of an independent Kurdish state in part of Turkey, Iraq, Iran and Syria. Turkey may be hoping by this attack on Afrin to strengthen the position of the latter in northern Syria.
"The uncontrolled delivery of modern weapons, including the reported delivery of man-portable air defense systems, by the Pentagon to the pro-U.S. forces in northern Syria, has contributed to the rapid escalation of tension in the region and resulted in the launch of the special operation by Turkish troops", it added. "Everyone's efforts need to aim at making progress in the political process", he said.
Recent statements by United States military officials about plans to train border security forces that would protect a Kurdish enclave in Syria also provoked Turkey's ire.
Washington had previously called on Ankara to refrain from launching a military incursion in Syria.
YPG spokesman Birusk Hasaka said clashes between Kurdish and Turkey-backed forces persisted on the third day of the operation.
It was being carried out under the framework of Turkey's rights based on global law, UN Security Council's decisions, self-defense rights under the UN charter and respect to Syria's territorial integrity, the military added. In that, it has the backing of the United States, a country that is also an ally of Turkey in the fight against the jihadist group.
YPG fighters based further east, in Jazira (Turkish Cezire), had been key to taking back Raqqa province from ISIL, and Kurds likely feel betrayed that the USA hasn't stood up for them more against Turkey. "Our top levels are engaged...and we're working through it", Mattis said.
The battle of Afrin has been long anticipated, as Turkey made clear that it was going to unleash an offensive, along with the Ankara-backed Syrian rebels, against the YPG in Afrin.