An air raid on a village in northeast Syria held by the Islamic State jihadist group killed at least 10 civilians including three children on Tuesday, a Britain-based monitor said.
The Syrian Observatory for Human Rights said the strikes on Tal al-Shair in the northeastern province of Hasakeh were carried out by the US-led coalition fighting IS in Syria and neighbouring Iraq since 2014.
The coalition's press office told AFP it was aware of the allegations but did not have records of carrying out strikes in the area.
It is the latest in a series of raids on the area that have reportedly caused civilian casualties in past weeks.
Tal al-Shair lies in a small pocket still held by IS fighters near the Iraqi border in the south of Hasakeh, where a Kurdish-Arab alliance backed by the coalition has been battling the jihadists in recent days.
According to the Observatory, a coalition air strike last week killed 11 civilians in the same IS-held area, and another 12 lost their lives in coalition raids on June 1.
The coalition told AFP it was carrying out an investigation into the June 1 allegation.
Earlier this month, it admitted to nine more civilians deaths, bringing to 892 the total number of civilians it acknowledges to have killed since it intervened in Iraq and Syria.
Monitors like the Observatory and Airwars say the toll is much higher.
The Observatory, which relies on sources inside Syria, says it determines whose planes carried out strikes according to type, location, flight patterns and munitions involved.
IS has lost most of the cross-border caliphate it declared in 2014.
In Syria it was pushed back by separate offensives -- one by Russia-backed regime troops and another by the US-backed Syrian Democratic Forces alliance.
But the jihadists still hold slithers of eastern Syria and have a presence in the vast Badiya desert running from the centre of the country to the border with Iraq.
More than 350,000 people have been killed in Syria's war since it started in 2011 with a brutal crackdown on anti-government protests.
It has since spiralled into a complex conflict involving world powers and foreign jihadists.
Syrians inspect the damaged of buildings on June 11, 2018 following reported air strikes by pro-government forces in the town of Binnish in Syria's northwestern Idlib province