Syria's new authorities under interim President Ahmed al-Sharaa have sought to disband armed groups
The Syrian Observatory for Human Rights war monitor has reported that 745 Alawite civilians were killed in Latakia and Tartus provinces.
Syrian authorities said the violence began when remnants loyal to Assad launched a deadly and well-planned attack on their forces on Thursday.
There were no immediate claim of responsibility for the attack.
Sharaa was appointed Wednesday to lead Syria for an unspecified transitional period
No group has claimed the four activists' abduction and they have not been heard from since.
Ankara-backed rebels played a key role in supporting Sharaa's Islamist group Hayat Tahrir al-Sham (HTS), which headed a rebel alliance that seized Damascus on December 8, toppling longtime ruler Bashar al-Assad.
The seismic change in Syria is expected to yield deeper Turkish sway just as a change of US administration is raising questions over how long Washington will keep backing the country's Kurdish-led forces.
Assad fled Syria following a lightning offensive spearheaded by the Islamist Hayat Tahrir al-Sham (HTS), more than 13 years after his crackdown on democracy protests precipitated one of the deadliest wars of the century.
At least 11 civilians were killed in Syria's second city Aleppo in one of the highest single tolls since a fragile truce came into force, a monitor says.
Syrian rebels seize control of the Islamic State group's main supply route to Turkey, a monitor says.
Greek authorities are gearing up to send hundreds of failed asylum-seekers back to Turkey, which is racing to set up reception centres under a controversial EU deal.
Syrian troops find a mass grave containing about 40 bodies in the city of Palmyra following its recapture from IS group.
Syrian troops backed by Russian forces recapture the famed ancient city of Palmyra from the Islamic State group in a major victory over the jihadists.
The second-in-command of so-called Islamic State (IS) has been killed in a US operation in Syria, US media report.
Russia will continue air strikes in Syria despite the withdrawal of most of its forces, a senior official has said.
EU and Turkish leaders seek to turn into a lasting accord a plan on easing Europe's migrant crisis hailed as a game-changer by Ankara and Brussels but swiftly criticised by the UN's refugee chief.
The UN says it plans to deliver aid to about 150,000 Syrians in besieged areas over the next five days amid a partial truce in the country's civil war.
EU ministers meet in Brussels later amid warnings the migrant crisis could threaten the bloc's survival.
