It was the first time that coalition aircraft had targeted IS in the Madajen area, where it has been fighting Al-Qaeda loyalists of Al-Nusra Front and their allies, the Syrian Observatory for Human Rights said.
The area lies between the IS stronghold of Dabiq and the town of Marea to the southwest, which is held by its rivals.
"At least 12 coalition strikes hit IS positions and weapons depots in areas that had never been targeted before," said Observatory director Rami Abdel Rahman.
Signup to our newsletter and follow us on Facebook and Twitter!
"The strikes might help the rebels and Al-Nusra Front in their fight against IS," he added.
Al-Nusra and its allies have been battling IS in Aleppo province and some others parts of Syria since January.
The drive by IS to assert its dominance in rebel-held areas which culminated in its declaration of a "caliphate" straddling Iraq and Syria in June prompted armed resistance from the rival rebel groups.
Washington launched an air campaign against IS in Iraq in August, extending it to Syria the following month with the support of Arab allies.