At least 10 Syrian soldiers were killed on Tuesday in clashes with Islamic State group jihadists in the eastern province of Deir Ezzor, a monitor said.
The Britain-based Syrian Observatory for Human Rights said the deaths came in fighting in Hawijat Sakr on the Euphrates River.
The clashes took place not far from Deir Ezzor military airport, a key remaining post for the Syrian army in the oil-rich province.
The Islamic State controls the majority of the province, but parts of the provincial capital, Deir Ezzor city, are still in government hands, along with the airport.
Deir Ezzor has been a key target of strikes against IS by the US-led coalition fighting the jihadist group in Syria and Iraq.
When the raids began, IS withdrew from several of its positions, and there have been few reports of active clashes involving the group in the province since.
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Elsewhere in Syria, the Observatory reported at least 12 people killed in Syrian regime air strikes on the Ain Tarma area outside the capital Damascus.
Among the dead were three children, the Observatory said.
The neighbourhood to the east of Damascus is under rebel control and is one of the areas regime forces have been battling to recapture from the opposition around the capital.
Although government forces control Damascus, rebels often fire missiles into the city from several strongholds on its outskirts.
On Tuesday, the regime also carried out air strikes against Irbin, another rebel-held area east of Damascus, the Observatory said.
The strikes killed five people, although the group said the toll was likely to rise because several of the wounded were in serious condition.