They died in "regime air strikes on the Shuhail district in the east of Deir Ezzor province targeting a health facility and other areas in the district", the Syrian Observatory for Human Rights said.
Dozens including children were wounded and the number of casualties is likely to rise, Observatory chief Rami Abdel Rahman said.
IS controls most of oil-rich Deir Ezzor province, he said, as well as more than half of its provincial capital.
The Britain-based Observatory relies of a wide network of sources inside Syria to gather its information.