At least 16 security personnel were killed on Thursday by gunmen loyal to Syria’s ousted dictator Bashar al-Assad, a war monitor said, in one of the deadliest clashes for Syria’s new leaders since the collapse of the Assad government.
The attack in Latakia Province, long a stronghold for Mr. al-Assad along Syria’s Mediterranean coast, set off an hourslong clash between government forces and the gunmen. It also prompted protests across the coastal region, with thousands calling on government forces to withdraw from the area.
“I heard some demonstrators threatening to return with weapons,” said Alaa Mousa, 30, a resident of Tartous, a port city. He said he felt like “the situation is on the verge of collapse.”
The clashes were among the most violent since a rebel coalition toppled the Assad government in December and installed an Islamist transitional government that has sought to exert its authority across the fractious country.
The coastal region has emerged as one of the most challenging areas for the Sunni Muslim-led government. It is the heartland of Syria’s Alawite minority, which includes the Assad family. The Alawites, who practice an offshoot of Shiite Islam, make up around 10 percent of Syria’s population and dominated the ruling class and upper ranks of the military under the Assad government.
The flaring tensions have become a critical test for the country’s new leaders.
Ibrahim al-Assil, a senior fellow at the Middle East Institute in Washington, said that if government forces “act in a disciplined manner, they might succeed in restoring order and maintain popular support.” But, he said, if “individual fighters or rogue units engage in revenge attacks against locals, the situation could spiral into sectarian clashes, further destabilizing the country.”
The clashes began Thursday afternoon as security personnel for the new government were conducting an operation in the countryside of Latakia, according to the war monitor, the Syrian Observatory for Human Rights. The security personnel were trying to arrest an official from the Assad government, according to a government official who asked to remain anonymous because he was not authorized to speak to the press.
Upon leaving one village, Beit Aana, the government forces were ambushed by gunmen and several were killed, according to two village residents.
The ambush sparked additional clashes between government forces and armed men loyal to Mr. al-Assad in that village and surrounding areas, according to the Syrian Observatory.
Artillery and machine-gun fire were heard throughout the afternoon, and at least one helicopter fired on the village, according to the war monitor and the two residents. The chaos prompted hundreds of people from Beit Aana and nearby villages to flee to the nearby countryside, the residents said.
It was not immediately clear if any civilians or the gunmen were killed.
The clashes prompted protests across Syria’s western coast, with thousands pouring into the streets of Latakia City, the provincial capital, and nearby Tartous, and calling for government forces to withdraw from the Latakia countryside.
In Tartous, protesters gathered around Al-Assadi Square, chanting “One, one, one — Tartous and Jableh are one,” referring to the area, Jableh, where the clashes had unfolded, according to residents. Outside one government building, government security forces fired into the area to try to disperse the crowd.
Protests by people who support the new government also erupted in major cities, including Homs and Idlib. The rebel coalition now in control of Syria governed Idlib in the later years of the country’s civil war.
On Thursday evening, the Syrian authorities announced a curfew from 10 p.m. to 10 a.m. Friday in many major cities, according to the Syrian Arab News Agency, the state media. The government also deployed additional security forces to the coast.
Late Thursday night, most streets in Tartous had emptied, with people obeying the curfew. But the city remained tense.
“This calm seems to be the calm before the storm,” Mr. Mousa said.
Reham Mourshed contributed reporting.
