The group, formerly known as the Nusra Front, could not immediately be reached for comment.
According to Reuters, the Observatory said the air strike had targeted a Fateh al-Sham base in a rebel-held area west of Aleppo, and it was not clear if it had been carried out by Russian or U.S. planes. The Nusra Front renamed itself Fateh al-Sham last year when it formally dissolved ties to al Qaeda.