The Syrian army ordered civilians to evacuate neighbourhoods of Aleppo on Thursday after fighting with Kurdish forces entered its third day, deepening the rift between the Syrian government and the US-backed Kurdish authorities in Syria.

The Syrian government urged people to leave the three contested neighbourhoods of Sheikh Maqsoud, Ashrafieh and Bani Zeid by early afternoon, opening humanitarian corridors and displacement shelters to facilitate their exit. The Syrian army said it would begin military operations against the Kurdish-led Syrian Democratic Forces (SDF) after the deadline, and issued maps showing specific areas that needed to be evacuated.

Shortly after the deadline expired at 1.30pm local time (1030 GMT) the Syrian government began shelling, with the SDF firing as well.

The clashes are the most intense fighting in Syria since the fall of the Assad regime in December 2024, and sparked fears of a broader conflict between the Syrian government and the well-armed Kurdish authorities who control much of north-east Syria – nearly a third of Syrian territory.

Despite an agreement for the SDF to merge into the Syrian army by the start of 2025, clashes have continued to erupt between it and the government. This week’s three days of fighting represent the longest open conflict between the two sides since the agreement was signed in March 2025.

About 140,000 civilians have been displaced by the fighting since it started on Tuesday, according to the directorate of social affairs and labour in Aleppo. At least eight civilians have been killed in the Kurdish-majority neighbourhoods, and seven civilians and one soldier killed in government-controlled areas. Dozens more have been wounded on both sides.

The SDF currently controls the Kurdish-majority neighbourhoods in Aleppo but on Wednesday the Syrian government announced its intention to push out Kurdish fighters from all of Aleppo city, in a move likely to exacerbate tensions between it and the Kurdish bloc in the north-east. The SDF denies having any fighters in the neighbourhoods, instead describing them as local self-defence forces.

Both sides accused the other of human rights violations, with the Syrian government claiming the SDF used civilians as human shields, not letting them evacuate and shooting at them when they tried. The SDF shared videos of what it said were government forces shelling a hospital in Aleppo, as well of what it called “brutal artillery shelling” targeting populated residential areas in Sheikh Maqsoud.

Many displaced people fled to other provinces of Syria, but some did not have the means to travel and sheltered in nearby mosques and churches.

At the root of the conflict are continuing disagreements about the status of the SDF in post-Assad Syria. It controls nearly a third of the country and has been a partner of US forces in their anti-Islamic State mission in Syria.

Under the 10 March agreement, the SDF is meant to integrate fully into the new Syrian army. However, disagreements over how exactly that integration would take place have stalled progress.

The SDF is seeking autonomy under the government, and after massacres on Syria’s coast and Druze-majority areas – in which some government-backed forces committed human rights violations against civilians – it has become more bullish on retaining its weapons. Some of the factions that make up the new Syrian army have been fighting the SDF for years and there is bitter enmity between them.

A meeting on Sunday between Damascus and the SDF yielded no new progress on implementing the agreement, despite the deadline expiring.

There is growing distrust on both sides, which has been worsened by fighting and a lack of progress in negotiations. Supporters of the government were outraged as pictures of civilians allegedly killed by SDF shelling circulated on social media, while thousands of protesters gathered in Qamishli, the de-facto capital of the SDF-controlled areas in north-east Syria, in solidarity with the SDF.

Describing Syrian government forces as “jihadists”, Farhad Shami, a spokesperson for the SDF, said on Thursday afternoon that fighting in Aleppo “opened the door to the expansion of the war into other areas”.

A US state department official on Thursday urged restraint on all sides, and said the US envoy to Syria, Tom Barrack, was trying to mediate between the two sides.

“All parties should focus on how to build a peaceful, stable Syria that protects and serves the interests of all Syrians, rather than pushing the country back into a cycle of violence,” the state department official said in a statement.

The US has tried to maintain a balancing act between its longtime Kurdish allies in Syria and the new authorities in Damascus, to which it has grown closer.

The SDF views US support and its continued military presence as a safeguard against Turkey, which has carried out three invasions against it. Turkey considers the SDF a Syrian offshoot of the Kurdistan Workers’ party (PKK), a Kurdish separatist group with which it has fought a four decades-long insurgency.

The Turkish foreign minister, Hakan Fidan, called the SDF the “biggest obstacle to peace in Syria” on Thursday, while the Turkish defence ministry said it would provide military aid to the government in Damascus if requested.