DAMASCUS, Syria (Reuters) – Syrian leader Ahmed al-Sharaa called for peace on Sunday after hundreds were killed in some of the deadliest violence in 13 years of civil war, pitting loyalists of deposed president Bashar al-Assad against the country’s new Islamist rulers.

The clashes, which a war monitoring group said had already killed 1,000 people, mostly civilians, continued for a fourth day in Assad’s coastal heartland.

A Syrian security source said the pace of fighting had slowed around the cities of Latakia, Jabla and Baniyas, while forces searched surrounding mountainous areas where an estimated 5,000 pro-Assad insurgents were hiding.

Al-Sharaa, the interim president, urged Syrians not to let sectarian tensions further destabilize the country.

“We have to preserve national unity and domestic peace, we can live together,” Sharaa said in a circulated video, speaking at a mosque in his childhood neighborhood of Mazzah in Damascus.

“Rest assured about Syria, this country has the characteristics for survival… What is currently happening in Syria is within the expected challenges.”

Rebels led by Sharaa’s Sunni Islamist Hayat Tahrir al-Sham group toppled Assad’s government in December. Assad fled to Russia, leaving behind some of his closest advisers and supporters, while al-Sharaa’s group led the appointment of an interim government and took over Syria’s armed forces.

Assad’s overthrow ended decades of dynastic rule by his family, which were marked by severe repression and a devastating civil war that began as a peaceful uprising in 2011.

The war — in which Western countries, Arab states and Turkey backed the rebels while Russia, Iran and militias loyal to Tehran backed Assad — became a theater for proxy conflicts among a kaleidoscope of armed factions with different loyalties and agendas. It has killed hundreds of thousands of people and displaced millions of Syrians.

After months of relative calm following the ouster of Assad, violence spiraled this week as forces linked to the new Islamist rulers began a crackdown on a growing insurgency from Assad’s Alawite sect in the Mediterranean provinces of Latakia and Tartous.

The Syrian Observatory for Human Rights, a British-based war monitor of unclear funding, said on Saturday that more than 1,000 people had been killed in the two days of fighting. It said that the victims included 745 civilians, 125 members of the Syrian security forces, and 148 fighters loyal to Assad.

Rami Abdulrahman, the head of the observatory, said the civilians included Alawite women and children.

Abdulrahman told Reuters on Sunday that the death toll was one of the highest since a chemical weapons attack by Assad’s forces in 2013 killed some 1,400 people in a Damascus suburb.

The European Union, whose officials have met al-Sharaa since he became de facto leader of Syria, condemned “all violence against civilians” and “any attempts to undermine stability and the prospects for a lasting peaceful transition” in Syria.

Syrian security sources said at least 200 of their members were killed in the clashes with former army personnel owing allegiance to Assad after coordinated attacks and ambushes on their forces that were waged on Thursday.

The attacks spiraled into revenge killings when thousands of armed supporters of Syria’s new leaders from across the country descended to the coastal areas to support beleaguered forces of the new administration.

The authorities blamed summary executions of dozens of youths and deadly raids on homes in villages and towns inhabited by Syria’s once-ruling minority on unruly armed militias who came to help the security forces and have long blamed Assad’s supporters for past crimes.

Clashes continued overnight in several towns where armed groups fired on security forces and ambushed cars on highways leading to main towns in the coastal area, a Syrian security source told Reuters on Sunday.

A security source added that the pro-Assad insurgents had staged hit-and-run attacks on several public utilities in the last 24 hours.

They damaged a main power station that cut electricity across parts of the province, while a main water pumping station and several fuel depots were disrupted.

“They are now trying to create havoc, disrupt life and attack vital installations,” he added.

In Latakia, police mounted new checkpoints inside the city. Two residents said that sounds of gunfire and artillery could be heard on the outskirts of the coastal city.

The Damascus authorities were also sending reinforcements to beef up their security presence in the mountainous province, where thick forests in rugged terrain were helping the anti-government fighters, another police source said.