Air strikes by the Syrian military have killed at least 30 people in the northwestern province of Latakia overnight, and the northern city of Raqa, according to the Syrian Observatory for Human Rights.
The attacks are seen as an effort by President Bashar al-Assad to prevent armed rebels fighting him from advancing on communities in the stronghold region of his Alawite sect.
In-depth coverage of escalating violence across Syria
"The toll in several air strikes on the town of Salma in Jabal Akrad rose to at least 20 people," Rami Abdel Rahman, the London-based watchdog group's director, told AFP news agency early on Saturday.
He said that 10 of those killed were believed to be civilians, although many of the bodies were so badly disfigured that it was not immediately possible to identify them.
At least six of those killed were Syrian rebel fighters, while four were foreign volunteers, he said.
Al Jazeera cannot independently verify Abdel-Rahman's account of the Latakia violence.
Seven children were among at least 13 civilians killed in an air raid on Raqa, the only provincial capital in rebel hands, the Syrian Observatory for Human Rights later reported.
'Army hitting back'
In recent days, rebel forces have captured a number of villages in Jabal Akrad, a mountainous district in the north of Latakia.
Assad's army has hit back, prompting fierce fighting that has left dozens dead on both sides, according to the Syrian Observatory.
Assad has deployed extra forces in the region and the air raids reflected an urgent priority to protect the main region of his Alawite sect, who account for 12 percent of Syria's 21 million people.
The Syrian Observatory also said that government troops stormed a village overnight, killing 12 people in Aleppo province.
In other violent incidents, fierce fighting erupted during the night between government troops and rebels in the Barzeh neighbourhood of Damascus, the group said, adding that the army shelled both Barzeh and the Jubar districts of the Syrian capital.
A car bomb exploded in Shaghur district in Damascus late on Saturday, wounding several people, three of them children, said the Observatory.
Al-Nusra Front and other rebel fighters in the eastern city of Deir Ezzor took control of the offices of Syria's ruling Baath party in the Howeika district, sparking regime bombardment, the Observatory said.
The regime controls much of southern and central Syria, while fighters hold northern areas near the Turkish border and along the Euphrates valley towards Iraq.
The northeast corner of the country is now an increasingly in Kurdish control.