The Syrian Observatory for Human Rights has issued a report today covering the civilian death toll of US-led coalition airstrikes in Syria over the past month, from May 23 to June 23, reporting at least 472 civilians, the largest in any 30-day period since the US started bombing Syria in 2014.

The attacks covered two provinces in Syria, with 222 civilians killed in Deir Ezzor, and the other 250 civilians killed in the Raqqa Province. Strikes against the area immediately surrounding Raqqa were nominally done in support of the Kurdish YPG’s advance on ISIS’ capital, the city of Raqqa.

In Deir Ezzor, much of the death toll was in airstrikes against buildings in the city of Mayadin, where huge numbers of civilian relatives of ISIS fighters were said to be killed, many of them young children. Over the two provinces, the Syrian Observatory counted 137 children killed in the US-led attacks.

These are just the figures from the reckoning of the Syrian Observatory, but they’ve usually roughly in line with the figures from other NGOs like Air Wars. The Pentagon’s own official toll likely won’t come for that period of time for a few months, though Pentagon figures usually ignore at least 90% of the dead civilians. Even acknowledging 10% of the NGOs’ toll, however, would be the worst month by their reckoning as well, reflecting how much worse the civilian toll is getting.