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 U.S.-led international coalition battling Islamic State carried out the air strike and that it killed 14 civilians and wounded 32 others.
A spokesman for the coalition said on Tuesday it had not carried out such a raid, and that its only strike in the vicinity in recent weeks took place in September across the Euphrates from the city.
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, Iran and Shi‘ite militias, is fighting Islamic State 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 U.S.-backed coalition has been conducting air strikes against Islamic State in support of the Syrian Democratic Forces (SDF) alliance of Kurdish and Arab militias to the east of Deir al-Zor across the Euphrates.
The rival U.S.-backed and Syrian army offensives against Islamic State have clashed several times over recent months as they have pushed the jihadists from territory in eastern Syria.
The U.S. and Russia have said they communicate with each other to prevent possible points of conflict of violence between the two offensives.