"At midnight on Sunday, 26 people were killed, including six women and eight children, when what appears to have been a surface-to-surface missile struck the village of Kfar Hamra," said the Observatory.
"Regime forces have taken surrounding orchards and are trying to take the village, and then to break the rebel siege of Nubl and Zahra," two villages north of Aleppo, the Britain-based watchdog added.
The Syrian army launched in the past few days an offensive in the north of the country with the aim of advancing on Azaz, a rebel stronghold 45 kilometres (28 miles) north of Aleppo.