Clashes erupted overnight in a rebel-held enclave outside Damascus, which was also hit by government air strikes despite a truce deal, a monitor said on Wednesday.
An internationally brokered ceasefire zone covering parts of Eastern Ghouta went into effect on Saturday.
The Syrian Observatory for Human Rights said the overnight fighting was the first in the enclave since the truce began.
Government troops clashed with fighters of the Faylaq al-Rahman rebel group in the Ain Tarma district, the Britain-based monitoring group said.
The fighting subsided by Wednesday morning but government warplanes then carried out strikes in the area.
Faylaq al-Rahman is allied with former Al-Qaeda affiliate Fateh al-Sham Front and the pro-government Al-Watan newspaper reported on Monday that it was excluded from the truce.
Government air strikes also hit the Utaya district of Eastern Ghouta, killing a girl and wounding seven other civilians, as well as the town of Zamalka, the Observatory said.
The new strikes came after two days of government air raids on the town of Arbeen in Eastern Ghouta, which killed 12 civilians, among them children.
The so-called "de-escalation" zone deal, hammered out by government allies Russia and Iran and rebel backer Turkey in May, covers only part of Eastern Ghouta, a large region that is key opposition territory.
A map displayed at a Russian defence minis try briefing appeared to show that the areas hit late on Tuesday and on Wednesday were inside the ceasefire zone.
"The air strikes and the clashes are a violation of the truce," Observatory director Rami Abdel Rahman said.
On Tuesday, a Russian military official denied that any air strikes had hit inside the ceasefire zone, which is being monitored in part by Russian police.
The Russian defence ministry map appears to show at least part of Arbin may be excluded from the truce zone.
Eastern Ghouta is the second of four proposed ceasefire zones to be implemented, after parts of the southern provinces of Daraa, Sweida and Quneitra.
More than 330,000 people have been killed in Syria since the conflict began with anti-government protests in March 2011.