Turkish-backed Syrian rebels have retaken a key town from Bashar al-Assad’s forces in the country’s last opposition-held territory of Idlibas fighting continues despite growing international calls for a ceasefire.

Videos sent by rebel fighters in the town of Saraqib on Thursday showed men cheering and waving the flag of the Syrian opposition on otherwise empty streets strewn with rubble and other debris.

The loss of the town, which is strategically located at the crossroads of Syria’s main two highways, is the first major setback for advancing Syrian government troops since Turkey decided to deploy soldiers and equipment to bolster rebel groups earlier this month.

However, the counteroffensive could be short-lived as the Syrian army and allied militias, accompanied by Russian airpower, continue a ferocious three-month assault on rebels and jihadist factions in the last part of the country that remains outside Assad’s de facto control.

The regime has retaken almost the entire southern part of Idlib province after the capture of more than 20 villages on Thursday, state media and opposition activists said.

Turkish attempts to hold a four-way summit with the leaders of Russia, France and Germany next week to address the escalating violence have been met with indifference by the Kremlin. The UN security council, where Moscow has systematically vetoed truce initiatives in the Syrian war, is due to meet again on Thursday to discuss Idlib, which has become the worst humanitarian crisis to date in Syria’s nine-year war.

More than 400 civilians have been killed and almost 1 million people have fled north towards the relative safety of areas closest to the Turkish border since December, according to the UN. About 80% of that number are women and children.

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About 170,000 people are sleeping rough in abysmal winter conditions as aid agencies struggle to provide enough food, tents, fuel and medicine. Schools, mosques, sports centres and even building sites are all full to bursting with displaced families, many of whom have already fled violence elsewhere in the country. With the Turkish border closed to refugees, there is nowhere else left to go.

Bombing of Idlib city and nearby towns earlier this week killed 20 civilians, including nine children and three teachers, after Syrian and Russian airstrikes hit eight schools and nurseries, among other targets, in a single day.

Facebook Twitter Pinterest Syrian rebels in Saraqib. The loss of the town is a major setback for the Assad regime. Photograph: Ghaith Alsayed/AP

“Some of the injuries were amputations, neurological injuries, and many other injuries. It was a hysterical situation in the city. Along with the sound of bombings and the sound of sirens, people had panic attacks. It was a difficult, bloody day,” said a surgeon at Idlib surgical hospital, which is supported by Médecins Sans Frontières.

Two more hospitals – Idlib Central and Mareet Misirin – also experienced near misses, as missiles and artillery shells fell less than 100 metres away from the facilities.

At least one internationally funded educational centre in the area has suspended its work as a result of Tuesday’s airstrikes on schools, said Máiréad Collins, Christian Aid’s senior advocacy adviser for Syria.

Idlib province and the surrounding countryside are technically protected by a de-escalation deal brokered by Ankara and Moscow in 2018. The agreement began to break down last year, after control of most of the area was wrested from more moderate rebel groups by Hayat Tahrir al-Sham (HTS), formerly al-Qaida’s Syrian affiliate.

Despite warnings from the UN and aid agencies that fighting in Idlib would put 3 million civilians at risk, Damascus launched an attritional and then full-scale campaign on the province, arguing that HTS was not covered by the de-escalation deal.

In early February Turkey took the unprecedented step of deploying approximately 12,000 troops to shore up the deal and protect the border, leading to the first direct clashes between Turkish and Syrian government forces in the war.

Twenty Turkish military personnel have been killed in the counteroffensive, the Turkish defence ministry said on Thursday. Ankara and Moscow are discussing opening Idlib’s airspace to both armed and unarmed Turkish drones, the Turkish defence minister, Hulusi Akar, was quoted as saying, but he added that problems over the issue persisted.

The Turkish president, Recep Tayyip Erdoğan, has vowed Ankara will not take the “smallest step back” in the standoff with Damascus and Moscow over Idlib, giving the regime until the end of the month to pull back.

