The Britain-based Syrian Observatory for Human Rights, an opposition war monitor, said Israeli strikes hit missile depots for Lebanon's militant Hezbollah group in Aleppo's southern suburb of Jibreen, near the Aleppo International Airport, and the nearby town of Safira, home to a sprawling military facility.
The observatory said 36 Syrian troops and six Hezbollah fighters died, and dozens of people were wounded, calling it the deadliest such attack in years.
There was no immediate statement from Israeli officials on the strikes.
Israel, which has vowed to stop Iranian entrenchment in its northern neighbour, has carried out hundreds of strikes on targets in government-controlled parts of Syria in recent years, but it rarely acknowledges them.
On Thursday, Syrian state media reported airs trikes near the capital, Damascus, saying they wounded two civilians.
Hezbollah has had an armed presence in Syria since it joined the country's conflict fighting alongside government forces.
Aleppo, Syria's largest city and once its commercial centre, has come under such attacks in the past that led to the closure of its international airport. Friday's strike did not affect the airport.
The strikes have escalated over the past five months against the backdrop of the war in Gaza and ongoing clashes between Hezbollah and Israeli forces on the Lebanon-Israel border.
