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.
Nato defence ministers will assess the "troubling escalation of Russian military activities" in Syria, the alliance's secretary-general says, ahead of talks in Brussels.
Russia says it has launched rocket strikes on Islamic State group targets in Syria from warships in the Caspian Sea - about 1,500km (930 miles) away.
At last Russia has decided that it will not be in the sidelines any more. After much speculation among western powers about its role in the four-year long Syrian war, Russia has come out full force to defend its long time regional ally, President Assad.
Islamic State militants in northern Syria have blown up another monument in the ancient city of Palmyra, officials and local sources say.
Putin's action is a clear message to the West that Russia is a world power to be reckoned with. He is ready to use his military power to back his diplomatic goals. He is also sending a message to the West to not meddle with Russia over Ukraine.
US President Barack Obama says the Russian bombing campaign in Syria in support of President Bashar al-Assad is driving moderate opposition underground and "only strengthening" Islamic State.
Donald Trump says he would send home all Syrian refugees the US accepts, if he becomes president.
Russia appears to have begun carrying out air strikes in Syria against opponents of President Bashar al-Assad, a US defence official says.
President Vladimir Putin secures parliament's unanimous backing to launch air strikes against Islamic State militants in Syria, paving the way for imminent Russian military intervention in its closest Middle East ally.
US President Barack Obama has said defeating Islamic State in Syria would only be possible if President Bashar al-Assad stepped down.
