An airstrike in eastern Syria early on Wednesday has killed at least 30 civilians and injured dozens more, the Syrian Observatory for Human rights has said.
The strike in al-Dablan, south-east of al-Mayadeen, is the second in 48 hours that has caused multiple fatalities.
On Monday, at least 57 people were killed when a suspected US-led coalition plane struck a jail run by the Islamic State group in eastern Syria, the observatory claimed.
The identity of the aircraft used in Wednesday's airstrike was not yet known, the observatory said.
The US-led coalition is supporting an offensive by Arab and Kurdish militiamen from the Syrian Democratic Forces (SDF) against the Islamic State group's self-declared "capital" of Raqqa, around 200 kilometres north-west of al-Dablan.
Russian and Syrian regime war planes have also been striking Deir az-Zor province, with pro-Damascus militias have embarked on a campaign against the group.
IS overran Raqqa in 2014, transforming it into the de facto Syrian capital of its self-declared "caliphate".
Earlier this month, the Syrian Observatory for Human Rights said US-led coalition airstrikes on two Syrian provinces targeting extremists have killed 472 civilians over the past month, more than double a previous 30-day toll.
The coalition insists it takes every measure to avoid hitting civilians, including by aborting missile strikes at the last moment if a civilian unexpectedly wanders into the target zone.
In an emailed statement, the international alliance said its forces "work diligently and deliberately to be precise" in their airstrikes, according to Reuters.
At least 320,000 people have been killed since Syria's conflict erupted in 2011 with anti-government protests, according to the UK-based observatory.
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