Less than two weeks after President Donald Trump sent Marines into Syria, the participation of the U.S. military in a coalition campaign inside that embattled country has entered the spotlight. A human rights group has reported a U.S.-led air attack that left 33 civilians dead.

The report indicated that U.S.-led coalition forces conducted an airstrike in northern Syria and hit a school that had been serving as a temporary shelter for displaced families, according to Agence France Presse. The school was located between two cities in northern Syria — Raqqa and Tabqa — that are currently controlled by ISIS.

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"We can now confirm that 33 people were killed, and they were displaced civilians from [Raqqa], Aleppo and Homs. Only two people were pulled out alive," said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights. The human rights group said the airstrikes had happened on Tuesday near the town of Al-Mansura. A Pentagon spokesman later said that the coalition would investigate the incident.

"Since we have conducted several strikes near [Raqqa] we will provide this information to our civilian casualty team for further investigation," the Pentagon said.

Human rights groups that monitor the U.S.-led military coalition campaign in Syria have fiercely disagreed with the tactics being used and their ultimate human cost. Although U.S. military sources claimed earlier this month that only 220 civilians had been killed by the coalition since 2014, the monitoring group Airwars put the number as high as 2,463 civilians — and perhaps even higher. In its statement, the military wrote "although the Coalition takes extraordinary efforts to strike military targets in a manner that minimizes the risk of civilian casualties, in some incidents casualties are unavoidable."