More than 40 civilians have been killed by aerial bombardment by the Syrian government in Idlib, according to a UK-based monitoring network.
At least 13 women and an unknown number of children were killed in the attacks in al-Laj village and Darkoush in Idlib, a northwestern province bordering Turkey, the Syrian Observatory for Human Rights said on Sunday.
The report issued by the Syrian Observatory cited activists as blaming Syrian government fighters for the deaths.
They said they expected the death toll to increase.
Al Jazeera cannot independently verify the Syrian Observatory's reports.
Fighting has been raging across Idlib province since Nusra Front and Islamist Brigade fighters on Saturday captured the town of Jisr al-Shughur, a last-remaining government stronghold, according to the Syrian Observatory.
Separately, it said four Syrian soldiers were killed by a missile fired from Israeli-occupied territory in the Golan Heights.
Rami Abdur Rahman, the Syrian Observatory's director, said it was not clear whether the missile was fired by a plane or from a vehicle.
For its part, the Israeli military said on Sunday it launched an air strike on its border with Syria after spotting fighters carrying a bomb in the Golan Heights.
It carried out the strike after troops saw "a group of armed terrorists" approach the border with an explosive intended to target Israeli troops.
It said that Israeli aircraft "targeted the squad, preventing the attack".
It did not offer any casualty figure for the strike.
Benjamin Netanyahu, Israeli prime minister, sent messages via Twitter commending the soldiers involved in the air strike.
"Any attempt to harm our soldiers and civilians will be met with a determined response like the military action tonight that thwarted a terror attack," he said.
No one immediately claimed responsibility for the alleged attack attempt.
In other Syria-related developments, fresh reports have emerged concerning the Assad government's alleged use of chlorine in attacks on civilians as recently as on March 16.
On April 16, Mohamed Tennari, a Syrian doctor, addressed the UN Security Council, moving some of its members to tears with a witness account and videos of suspected chlorine attack in Sarmin, also in Idlib province.
"He showed a video of a suspected chlorine attack March 16 in his town of Sarmin in Idlib province, with images of three children, ages 1 through 3, dying despite attempts to resuscitate them," the Syrian Observatory said in a report.
Reports of use of chlorine have also been made by Amnesty International, the UK-based rights watchdog group.
The Security Council last month approved a resolution to condemn the use of toxic chemicals in the country and threatened action against its use.
Source: Al Jazeera and agencies