Four women and two children were among the nine family members killed when a mortar round hit their home in Mashmashan village near the town of Jisr al-Shughur, the Britain-based Syrian Observatory for Human Rights said.
On Monday, 27 people were killed in violence across Syria, including at least 20 who died in twin blasts targeting security buildings in Idlib city, most of them security force personnel, the watchdog said.
UN chief Ban Ki-moon condemned what he called "terrorist bomb attacks" in both Idlib and Damascus.
He called on "all parties" in the Syria conflict to halt violence and work with the growing UN Supervision Mission in Syria to firm up a troubled ceasefire that went into force on April 12, UN deputy spokesman Eduardo del Buey said.
Two observers from a mission advance team of 30 are already deployed in Idlib province.
The mission will eventually grow to 300 observers to be spread across Syria, where the UN says well over 9,000 people have been killed since an uprising started against President Bashar al-Assad in March last year.