Seven civilians were killed and six others injured on Sunday during bombardments by the Syrian army in the last major rebel stronghold in the northwest, the Syrian Observatory for Human Rights said.
"Regime forces committed a massacre by directly targeting residential areas, using artillery shells and rocket launchers in Darat Izza, Aleppo province," said the Britain-based war monitor, which relies on a network of sources in the country.
"At least five civilians were killed in Darat Izza, and two other civilians in the locality of Abzimou" in the same province, it added.
Earlier, five government soldiers were killed by the Hayat Tahrir al-Sham group, formerly the local branch of Al-Qaeda, in the north of Latakia province, according to the Observatory.
It said the HTS attack was a response to the wounding of 14 civilians earlier on Sunday in Syrian army bombardments on residential areas of Idlib city.
HTS controls swathes of Idlib province and parts of the neighbouring Aleppo, Hama and Latakia.
The group, considered a terrorist organisation by Damascus, the United States and the European Union, regularly clashes with Syrian and allied Russian forces.
HTS is the main rebel organisation active in northwest Syria, but there are other groups, some backed by Turkey, and there have been fierce clashes in recent weeks.
In late November, Syrian government bombardments killed nine civilians, including six children, while they were harvesting olives in Idlib province, the Observatory said.
Started in 2011 after the repression of anti-government protests, the war in Syria has left more than half a million dead and displaced millions.
The Idlib region is subject to a ceasefire brokered by Russia and Turkey after a regime offensive in March 2020, but it has been repeatedly violated.