Syria’s leader vowed on Sunday to hunt down the perpetrators of violent clashes pitting loyalists of deposed President Bashar al-Assad against the country’s new Islamist rulers and said he would hold to account anyone who overstepped their authority.

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

In a speech broadcast on national television and posted on social media, Ahmed Sharaa, whose rebel movement toppled Assad in December, accused Assad loyalists and foreign powers that he did not name of trying to foment unrest.

“Today, as we stand at this critical moment, we find ourselves facing a new danger - attempts by remnants of the former regime and their foreign backers to incite new strife and drag our country into a civil war, aiming to divide it and destroy its unity and stability,” he said.

The top commander of a Syrian Kurdish armed group, whose forces are in a separate battle with Turkey, had earlier blamed Turkish-backed Islamist factions for some of the most disturbing violence: the reported executions of civilians belonging to Assad’s Alawite sect. Turkey did not immediately respond to the allegation.

At the United Nations in New York, diplomats said the United States and Russia have asked the Security Council to meet behind closed doors on Monday over the escalating violence in Syria.

Interim President Sharaa’s office said it was forming an independent committee to investigate the clashes and killings by both sides. Syrians have circulated graphic videos of executions by fighters. Reuters could not immediately verify the videos.

“We will hold accountable, with full decisiveness, anyone who is involved in the bloodshed of civilians, mistreats civilians, exceeds the state’s authority or exploits power for personal gain. No one will be above the law,” Sharaa added in the video speech after earlier calling for national unity.

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

Assad fled to Russia last year after rebels led by Sharaa’s Sunni Islamist Hayat Tahrir al-Sham group ousted his government, ending decades of severe repression and a devastating civil war. Some of his closest advisers and supporters were left behind.

Western countries, Arab states and Turkey backed the rebels and Russia, Iran and militias loyal to Tehran backed Assad in the civil war, which became a theatre 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.

Since Assad’s overthrow, Turkish-backed groups have clashed with Kurdish forces that control much of northeastern Syria. Israel has separately struck military sites in Syria, and is lobbying the United States to keep Syria weak, sources have told Reuters.

GROWING INSURGENCY

Relative calm followed Assad’s ousting, but violence has spiralled recently as forces linked to the new Islamist rulers began a crackdown on a growing insurgency from the Alawite sect.

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

Rami Abdulrahman, the head of the observatory, said 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.

Syrian security sources said more than 300 of their members had been killed in clashes with former army personnel owing allegiance to Assad in attacks that began on Thursday.

Syria’s SANA state news agency reported on Sunday that a mass grave containing the bodies of recently killed security forces had been discovered near Qardaha, Assad’s home town.

The attacks spiralled into revenge killings against Alawites, an offshoot of Shi’ite Islam that is the faith of some of Assad’s most ardent supporters and became associated with Assad’s wartime atrocities against Syria’s mostly Sunni Muslim population.

The United States as well as U.N. human rights chief Volker Turk called on Syria’s interim leadership to bring the perpetrators to justice.

RESIDENT SAYS HOMES BURNED

Mazloum Abdi, the Kurdish commander, said in written comments to Reuters that factions “supported by Turkey and Islamic extremists” were chiefly responsible for the violence, and asked Sharaa to hold them to account.

Damascus authorities have 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.

A resident of the town of Qadmous told Reuters that people in the town and surrounding villages had fled to nearby fields to protect themselves. He said a convoy of fighters with tanks, heavy weapons and small drones had burned homes and cars along the main road near his town.

“We don’t know how many people are killed yet because they haven’t gone home and don’t plan to for the next few days,” said the resident, who spoke on condition of anonymity for fear of reprisals.

A security source said pro-Assad insurgents had attacked several public utilities in the last 24 hours, disrupting electricity and water supplies.

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