Twenty-four civilians were killed by air strikes and artillery fire in the opposition-held Syrian province of Idlib on Tuesday, first responders say.
Nine people, including three children, died when warplanes bombed the town of Talmenes, the White Helmets reported.
Meanwhile the wife and three children of one of the group's volunteers were among six members of the same family killed when shells hit Badama village.
An air strike on the town of Maasaran reportedly killed another six people.
Idlib is the last major region still held by rebel fighters and jihadists opposed to President Bashar al-Assad.
The last farewell ... funeral and burial took place for wife and three daughters of White Helmet Anwar. The four were slain in a regime missile attack which targeted his house in the town of #Bdama, west of #Idlib this afternoon. pic.twitter.com/cGYekhbPMd— The White Helmets (@SyriaCivilDef) December 18, 2019
The United Nations estimates the region is home to three million people, including a million children. More than 40% of them come from other previously opposition-held areas.
A ceasefire negotiated by Russia, whose military campaign in support of Mr Assad has turned the tide of the eight-year civil war in his favour, and Turkey, which backs the opposition, halted a government assault on Idlib in August.
However, skirmishes and bombardments are still an almost daily occurrence.
On 7 December, air strikes on opposition-held areas reportedly killed 20 people. Nine of the deaths were in the village of Balyoun, where a market was hit.
Last month, the UN Office for the High Commissioner for Human Rights (OHCHR) said it had verified more than 1,000 civilian casualties in north-western Syria since April as a result of hostilities between pro-government and opposition forces.
Dozens of attacks against medical facilities and staff have also been verified.
The Syrian Observatory for Human Rights, a UK-based monitoring group, has said that more than 250 civilians have been killed since the ceasefire was agreed.