An air raid in the government-held Qusur district of Deir al-Zor city in eastern Syria killed more than a dozen people, Syrian state television and a war monitor said on Monday.
State television said jets from a US-led international coalition battling ISIS carried out the air strike and that it killed 14 civilians and wounded 32 others.
The war monitor, the Britain-based Syrian Observatory for Human Rights, reported that it was not known which aircraft carried out the strike, but that at least 22 people were killed.
The Syrian army, backed by Russia and Iran, is fighting ISIS in the city of Deir al-Zor, as well as in parts of the surrounding countryside. Both Syrian and Russian jets have been hitting Islamic State in that area.
The US-backed coalition has been conducting air strikes against ISIS in support of the Syrian Democratic Forces (SDF) alliance of Kurdish and Arab militias to the east of Deir al-Zor across the Euphrates.
Coalition spokesman Colonel Ryan Dillon said by phone that he would check the reports, but that there was no reason for coalition jets to strike targets in Deir al-Zor city because the SDF was not fighting there.
The rival US-backed and Syrian army offensives against ISIS have clashed several times over recent months as they have pushed the extremists from territory in eastern Syria.
The US and Russia have said they communicate with each other to prevent possible points of conflict of violence between the two offensives.
Deadly air strike hits Syrian govt-held Deir al-Zor