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.
Russia is considering whether to follow the US and its allies in conducting air strikes against Islamic State (IS) targets, President Vladimir Putin says.
France claims to have carried out its first air strikes against the Islamic State group in Syria following nearly three weeks of surveillance flights.
European Union leaders pledge another €1bn (£700m, $1.1bn) to help UN agencies support Syrian refugees in the Middle East, as part of renewed efforts to tackle the EU's migrant crisis.
Splits within the EU on the relocation of 120,000 migrants are further exposed as leaders gather for an emergency meeting in Brussels.
European Union ministers are to meet to try to resolve a dispute over how to relocate 120,000 asylum seekers who have recently arrived in Europe.
Syria's civil war has prompted the first withdrawal of crop seeds from a "doomsday" vault built in an Arctic mountainside to safeguard global food supplies.
The United States will increase the number of refugees it takes in by 15,000 over each of the next two years, bringing the total to 100,000 by 2017, US Secretary of State John Kerry says.
Austria saw the arrival of at least 10,000 migrants, amid bitter rows among EU nations on how to handle the growing crisis.
Migrants stranded in Croatia are making renewed efforts to head north despite moves by Slovenia and Hungary to hold them back.
Croatia closes seven of its eight road border crossings with Serbia following a huge influx of migrants.
