"More than 70 killed and dozens wounded and captured in bloody clashes and ambushes on the Syrian coast between members of the Ministry of Defense and Interior and militants from the defunct regime's army," the Syrian Observatory for Human Rights said in a post on X.
It said earlier that fighting on Thursday between government forces and Assad loyalists had killed 48 people in the coastal town of Jableh and adjacent villages, saying they were "the most violent attacks against the new authorities since Assad was toppled" in December.
Forces linked to Syria's new rulers have engaged in heavy fighting with fighters loyal to deposed President Bashar al-Assad in a coastal area of the country.
It is the worst violence in Syria since rebels toppled Assad in December and installed an Islamist transitional government.
A war monitoring group, the British-based Syrian Observatory for Human Rights, said more than 70 people have been killed.
A curfew has been imposed in the port cities of Latakia and Tartous, where the fighting has broken out.
The clashes started when government forces were ambushed during a security operation in Latakia.
Reinforcements have been sent, and videos posted online show heavy gunfire in some places.
The coastal region is the heartland of the Alawite minority, and a stronghold of the Assad family.
Estimations of the number of people killed in the violence vary, and the BBC has been unable to independently verify them.
Late on Thursday, Syrian-based Step news agency was reporting that government-aligned forces had killed "about 70" former regime fighters, while more than 25 others were captured in Jableh and surrounds.
There have also been reports of clashes in the cities of Homs and Aleppo.
The crackle of heavy gunfire on residential streets in Homs could be heard on unverified videos on social media.
A spokesman for Syria's defence ministry, Colonel Hassan Abdul Ghani, issued a warning to Assad loyalists fighting in Latakia via state media.
"Thousands have chosen to surrender their weapons and return to their families, while some insist on fleeing and dying in defence of murderers and criminals. The choice is clear: lay down your weapons or face your inevitable fate," he said.
The region has become a major security challenge for interim president Ahmed al-Sharaa.
Alawite activists said their community had been subjected to violence and attacks since Assad fell, particularly in rural Homs and Latakia.
He is also facing resistance in the south, where there have been clashes with Druze forces in recent days.
Earlier this week, Syria's foreign minister told the global chemical weapons watchdog that the new government was committed to destroying any remaining stockpiles produced under-Assad.
Assad's government denied ever using chemical weapons during the 14-year civil war, but activists accused it of carrying out of dozens of chemical attacks.
