The Syrian Observatory for Human Rights said Russian and Syrian warplanes on June 25 targeted the region of Al-Quriyah, southeast of the city of Deir Ezzor, RFE/RL reports.
It said 58 civilians were killed in the air strikes. It did not specify whether the 24 others killed were IS militants or civilians.
Read alsoIraqi commander: Fallujah 'fully liberated' from ISThe monitoring group had first reported that 47 people, including 31 civilians, had died in the raids.
IS militants control most of Deir Ezzor and have laid siege since March 2015 to the remaining government-held areas in the city of the same name, which is close to Syria's eastern border with Iraq.
Russian warplanes have been carrying out an air campaign in support of President Bashar al-Assad since September 2015.
More than 280,000 people have been killed since Syria's conflict erupted in March 2011.
