A Syria war-monitoring group says at least 12 pro-government fighters were killed in airstrikes the previous night in the country's east.
The Britain-based Syrian Observatory for Human Rights says none of the fatalities were Syrian nationals but foreign fighters.
Syria's government forces have relied on support from the Lebanese militant Hezbollah group and also regional militias organized by Iran to wage war on rebels and Islamic State militants.
In Damascus, government media reported early on Thursday that international coalition aircraft struck Syrian army positions near the front lines with IS in eastern Syria.
The Observatory says the U.S.-led coalition was likely behind the strikes but the Pentagon said it had "no information to substantiate those reports."