A bus has been attacked in eastern Syria, killing at least 28 people, reportedly soldiers.
Syrian state media said the bus was targeted on Wednesday in the restive Deir al-Zour province, saying it was "citizens" killed.
But other sources including a monitoring group said soldiers were on board, giving a higher death toll.
There was no immediate claim of responsibility for the attack.
The UK-based Syrian Observatory for Human Rights (SOHR) attributed the attack to the Islamic State (IS) jihadist group, saying 37 soldiers died.
Citing sources, the SOHR said the attack was a "well-planned ambush by Islamic State members, targeting three buses carrying pro-regime militiamen and soldiers".
Other sources cited by Reuters also said the buses carried Syrian state troops.
IS fighters and Syrian forces loyal to the government of Syrian President Bashar al-Assad often clash in the area, near the ancient city of Palmyra.
In 2014, IS imposed its brutal rule on millions of people, at one stage controlling 88,000 sq km (34,000 sq miles) of territory stretching from western Syria to eastern Iraq.
After five years of fighting, local forces backed by the US and its allies managed to wrest back all the territory controlled by IS.
IS was declared territorially defeated in Syria and Iraq in March 2019.
But its presence has endured in parts of Syria, which has been racked by a civil war since 2011 and IS cells continue to launch attacks. If confirmed the latest attack would be the deadliest this year carried out by the group, the SOHR said.
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