The heaviest fighting and shelling for months hit Hama province in northern Syria on Friday, a war monitor said, but there were diverging accounts of how the battle started.
The clashes were accompanied by heavy bombardment, with dozens of shells and rockets being fired, said the Britain-based Syrian Observatory for Human Rights, adding that it had confirmed there had been casualties.
The battle is around the village of Maan, 23 km north of Hama in western Syria, near the location of a rebel assault and government counter-offensive this spring.
The Observatory said the fighting arose from an attempt by pro-government forces to advance north from Maan into rebel territory.
A military media unit run by the government's ally Hezbollah, a Lebanese Shia group, said it was rebels who tried to attack, but were thwarted by the Syrian army.
Hardline Islamist groups, including the Tahrir al-Sham alliance which contains al Qaeda's former Syrian affiliate, are present in the area.
The war front in northern Hama province has mostly been quiet since a de-escalation process, brokered by the government's ally Russia and rebel backer Turkey took effect in early May.
The Syrian army's main focus since May has been its campaign in the east of the country against Islamic State.