The activists say the airstrike late Monday in Boukamal was most likely carried out by the US-led coalition that has been targeting the Islamic State group in Syria and Iraq.
Airstrikes by the US-led coalition have killed dozens of civilians over the past several weeks as the battle against the extremists intensifies.
The Britain-based Syrian Observatory for Human Rights said today that the airstrike killed 13 civilians, including women and children, as well as three IS fighters.
Opposition activist Omar Abu Laila, who is from the province where the strike took place and currently lives in Europe, said eight people were killed, including an Iraqi family of four.