A warplane from an unidentified air force has attacked the eastern Syrian village of Doblan, along the Euphrates River, according to the Syrian Observatory for Human rights, who said that cluster bomblets were dropped on the area, killing at least 30 civilians and injuring dozens more.

Doblan is just southeast of the city of Mayadin, which was just attacked yesterday by US forces, killing a large number of civilians destroying an ISIS-held prison. It is unclear, however, if the Doblan attack is a continuation of the US strikes, or some other nation’s involvement.

US-led coalition officials would not comment on the Doblan attack one way or the other, but when asked by other media outlets, they insisted they’d attacked Mayadin with meticulous planning to avoid killing civilians, though they have so far not acknowledged that it was even a prison.

Cluster bombs are a particular problem when used in populated areas, because many of the bomblets don’t detonate immediately, and can remain active on the ground long after the attack, causing additional civilian casualties. Both the US and Russia have refused to sign the global cluster bomb ban.