Fighting continues in some of the de-escalation zones created across stretches of eight provinces in Syria, however, war monitor says "hostilities have dropped".
Dozens of Daesh group fighters cornered in a northern part of Syria's Tabqa are holding off US-backed forces that hold almost all of the city, a monitor said Sunday.
Tabqa sits on the Euphrates River and on a strategic supply route about 55 kilometres (35 miles) west of Raqqa, the Syrian heart of Daesh's so-called caliphate.
In their drive for Raqqa, the US-backed Syrian Democratic Forces have captured more than 90 percent of Tabqa, but have not been able to fully clear the militants out of the city or the adjacent dam. A majority of the SDF is made up of fighters from YPG – a wing of the PYD which Turkey considers an affiliate of its local terror group, the PKK.
"The SDF hasn't been able to seize complete control of Tabqa because [Daesh] fighters are still present in the neighbourhoods of Wahdah and Hurriyah," said Rami Abdel Rahman, who heads the Syrian Observatory for Human Rights.
The two districts are in the city's north near Tabqa Dam, Syria's largest.
Abdel Rahman said "dozens" of Daesh fighters were laying mines and engaging in small-scale skirmishes with the SDF, but had not deployed suicide bombers in recent days.
An SDF commander inside Tabqa said on Sunday that his forces were locked in "violent clashes" in the northern part of the city.
"The operation is going slowly because of the presence of civilians being used as human shields by [Daesh]," the commander said, saying his forces were trying to advance "carefully and accurately".
"Soon we will be able to announce the city fully cleared of Daesh," he added.
The SDF first entered Tabqa on April 24, but Daesh has put up fierce resistance including using snipers and weaponised drones, a tactic it perfected in neighbouring Iraq.
The SDF has also revealed plans to expand their territory in northern Syria.
The group says it wants to push its territory westward in order to link northern Syria to the Mediterranean Sea.
It will ask the United States for political support in creating a trade corridor to the Mediterranean as part of a deal for their role in liberating Raqqa from Daesh, it said.
Turkey has called on the US to drop their support of the group, which it says is linked to the PKK.
Fighting subsided in Syria on Saturday after a deal signed by regime backers Russia and Iran and opposition supporter Turkey to create four "de-escalation zones" began to take effect.
The multi-phase plan, signed Thursday in the Kazakh capital Astana, is one of the more ambitious efforts to end Syria's six-year conflict.
It provides for a ceasefire, rapid deliveries of humanitarian aid and the return of refugees after "de-escalation zones" are created across stretches of eight Syrian provinces.
Those zones would see a halt to hostilities, including air strikes. The plan also proposes the deployment of "third-party" monitoring forces.
It began coming into effect at midnight (2100 GMT Friday), according to Russia, but co-sponsors have until June 4 to finalise the zones' borders.
The four main battlegrounds covered are the north-western province of Idlib, parts of central Syria, the south, and the opposition enclave of Eastern Ghouta near Damascus.
Some of those areas had already seen a drop in violence by Saturday, and Russia's defence ministry said Syria was "stable" at the end of the deal's first day.
Residents of the Syrian town of Maaret al Numan, who are in the Idlib safe zone, say the atmosphere is a little more relaxed, but some are still worried the regime will not respect the ceasefire.
"We noticed there are fewer aeroplanes, almost none. People are buying and selling more," said Abu Qais, a 26-year-old trader in Maaret al Numan in Idlib province.
"Psychologically, residents are relieved," he said.
"Regarding the ceasefire, we hope that the bloodshed of the Syrians will end and for a real truce," Abu Elias, a teacher, said. "But we have already tried ceasefires several times, and the criminal Assad regime has never respected them."
Syrian regime warplanes could be heard from Eastern Ghouta around midday, according to an AFP correspondent in the rebel-held town of Douma.
The Observatory said regime forces were clashing with rebels in the central province of Hama, dropping barrel bombs and firing artillery at opposition-held villages there.
"Despite these violations, we can still say that hostilities have dropped," Abdel Rahman said.
The Britain-based Observatory said a child was killed in regime shelling in parts of Homs province that fall within the de-escalation zones, the first civilian death in the zones since the deal began coming into effect.
Another seven opposition fighters were killed in other areas, up from an earlier toll of four.
Several ceasefires have been agreed since Syria's conflict broke out in 2011, but they have failed to permanently stem the fighting.
Fighting sanctioned under the new deal
The deal also calls for a continued fight against Daesh and former Al-Qaeda affiliate Fateh al Sham Front, which could pose challenges.
In Idlib province in particular, Fateh al Sham is a major component of the forces that control the area.
The Syrian regime and rebel groups are not signatories, and both sides spoke vaguely Saturday about "violations" of the agreement.
The Syrian National Coalition, a leading Syrian opposition body, elected prominent dissident Riad Seif, 70, as its new head on Saturday.
Seif, who spent eight years in a Syrian prison for his opposition activities, will replace Anas al-Abdeh.
Turkish army chief meets US counterpart
Turkey's Chief of General Staff Hulusi Akar met his US counterpart Joseph Dunford in Washington on Saturday where they discussed developments in Iraq and Syria.
The meeting was held ahead of a US visit by President Recep Tayyip Erdogan later this month.