Syrian TV broadcast footage of residents welcoming their troops in Tal Tamr by throwing flowers. The town is important given its strategic location on arterial highways to both Iraq and Turkey.
Some chanted "let Erdogan fail," referring to Turkey's president, while others held pictures of Syrian President Bashar al-Assad.
Asked whether he had spoken to Russian President Vladimir Putin, Syria's main military backer, about a deal between Damascus and Syrian Kurdish militias, Turkish President Recep Tayyip Erdogan said he didn't foresee a problem as Moscow, too, was "positive."
The deal between the Syrian Kurds and the Syrian government is a "military agreement to protect the borders of Syria against the Turkish aggression," Berivan Xhaled, co-chairwoman of the autonomous Kurdish administration of Ain Issa in Syria, told dpa.
Meanwhile sources close to the Syrian government told dpa that "all areas which will be entered by Syrian troops will fall immediately under the control of the Syrian government."
US President Donald Trump, who paved the way for the Turkish offensive against Washington's Syrian Kurdish partners by pulling back some troops last week, seems to be heading towards a complete military withdrawal from northern Syria.
A Kurdish military source said that Syrian troops and the Kurdish-led Syrian Democratic Forces (SDF) are to ensure security inside the border towns they take over, while Syrian soldiers are to control the frontiers.
He said the Russians were also part of the agreement, without giving details.
In Moscow, asked whether the offensive had the potential for direct conflict between the Turkish and Russian militaries, Putin's spokesman Dmitry Peskov replied: "We do not even want to think about such an option."
The Turkish and Russian militaries maintain communication channels specifically to prevent such a clash, Peskov said, according to state news agency TASS.
Washington is "preparing to evacuate" all its troops from northern Syria "as safely and quickly as possible," US Defence Secretary Mark Esper said in an interview Sunday with broadcaster CBS.
Esper's comments were a "positive approach," Erdogan said Monday, before leaving on an official visit to Azerbaijan. He also signalled that there seemed to be no change to US troop withdrawal plans.
There are about 1,000 US forces throughout north-eastern Syria.
The SDF was the main US partner in the fight against Islamic State but found themselves abruptly abandoned by Washington.
Turkey launched a long-threatened incursion into northern Syria on Wednesday, targeting Islamic State and the Syrian-Kurdish People's Protection Units (YPG), which Turkey considers to be linked to the outlawed Kurdistan Workers' Party (PKK), which is waging an insurgency on Turkish soil.
Erdogan insists that he is ensuring Turkey's border security and that he wants to resettle 1 to 2 million Syrian refugees in a buffer zone.
Turkish Defence Minister Hulusi Akar announced that the military had taken control of the border towns of Tal Abyad and Ras al-Ain.
SDF spokesman Mustafa Bali said Turkish troops had failed to advance into Ras al-Ain, while heavy clashes were ongoing on the southern outskirts of Tal Abyad.
Located in northern al-Raqqa province, Tal Abyad is where Kurdish fighters expelled Islamic State militants in June 2015.
Akar said there was only one prison holding Islamic State militants in the area that Turkey took over, adding that they were evacuated by the YPG and kidnapped before Turkish troops arrived. He didn't mention the exact location.
About 785 foreigners affiliated with Islamic State broke free on Sunday from Ain Issa camp, near al-Raqqa, Kurdish officials and a war monitor said.
"Europe had a chance to get their ISIS prisoners, but didn't want the cost. 'Let the USA pay,' they said," Trump tweeted Monday, adding that the "Kurds may be releasing some to get us involved. Easily recaptured by Turkey or European Nations [sic] from where many came, but they should move quickly."
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