He told Reuters the coalition would assess the report alleging civilian casualties, adding: "We have no further information at this time".
The area around al-Soussa, on the eastern bank of the Euphrates river, is still under the control of IS, which still retains pockets of territory near the border with Iraq.
He said the air strike had most likely been carried out either by the US-led coalition against ISIS or Iraqi forces that are working with it.
Most of the civilians were Iraqi, Observatory Director Rami Abdulrahman said.
Dozens of homes were destroyed, said SANA, accusing the US-led coalition of targeting local residents for refusing the entry of the US-backed Syrian Democratic Forces (SDF). The U.S. -led coalition does not directly coordinate with Assad, though it maintains a deconfliction line with his Russian ally.
U.S. and coalition planes in the eastern Syrian province of Deir Ezzor attacked a village along the Iraqi border which had some ISIS remnant forces within. Since Moscow's intervention in Syria in 2015, however, Iraq has also maintained a joint operations room with Iran, Russia and Syria.More news: U.S. Seeking to Delay Reuniting Immigrant Kids With Parents
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The Observatory said at least 30 Iraqi fighters were killed in the strike near the town of Albu Kamal on the Syria Iraq border.
The U.S. military did not respond to calls by The Associated Press for comments on the report.
Other times, however, the identity of the aggressor was less clear; last month, both the USA and Israel were blamed for deadly strikes that killed pro-Syrian government fighters in Deir Ezzor. In March, the Syrian Observatory for Human Rights assigned blame to the coalition for 2,967 civilian deaths.
Transparency group Airwars says that "almost all coalition strikes in early 2018-and claims of civilian harm-were now focused on eastern Syria".
ISI was largely defeated in most of the territory it controlled in both countries previous year, but fighters still operate in the desert near the border.