This article is more than 7 months old

This article is more than 7 months old

Fierce fighting in the last area of Syria that remains outside of Bashar al-Assad’s control has sparked the largest mass displacement of civilians in the war to date, leaving hundreds of thousands of people camped out in tents on the Turkish border in subzero conditions.

Around 700,000 people have fled a regime offensive against opposition-held north-west Idlib province since December, the UN said on Tuesday.

At the same time, clashes between the Syrian army and Turkish forces have moved the two countries closer to an all-out conflict than at any other point in the nine-year-old civil war.

Turkey’s president, Recep Tayyip Erdoğan, said on Tuesday that Damascus would pay a “heavy price” for any future attacks on Turkish troops, after the deaths of 13 Turkish military personnel in the area in the past week.

The two sides have traded artillery fire since Ankara sent reinforcements to Turkish observation posts in Idlib to secure its border and stem the bloodshed caused by the regime assault, which is being carried out with the help of Russian airpower.

As well as two deadly attacks on Turkish positions, dozens of Syrian government troops and allied militiamen have been killed in the escalation, according to the Syrian Observatory for Human Rights, a war monitor. The Turkish defence ministry said it had “neutralised” 101 Syrian regime troops, without giving evidence.

On Tuesday a Syrian helicopter was shot down, reportedly by rebel forces, killing all those onboard.

Facebook Twitter Pinterest Part of the wreckage of a Syrian regime helicopter shot down in Idlib province on Tuesday. Photograph: Ghaith Alsayed/AP

“The regime … got what it deserved in Idlib,” Erdoğan said at a televised ceremony in Ankara. “But it is not enough.” He said Turkey’s next steps in Idlib would be revealed publicly on Wednesday.

A Russian delegation sent to Ankara to try to negotiate a pause in the hostilities is believed to have left on Monday without any progress.

Erdoğan’s bellicose threat was echoed by his ruling coalition partner, Devlet Bahçeli, who said Turkey must be prepared to overthrow Damascus in response to the deaths of Turkish soldiers.

Turkey is seeking to enforce a de-escalation deal for Idlib brokered in 2018 by Moscow, which backs Assad, and Ankara, which supports some rebel groups in the area.

The ceasefire has been routinely broken by both sides, but an attritional Assad campaign has escalated since Hayat Tahrir al-Sham (HTS), formerly al-Qaida’s Syrian affiliate, seized control of most of the area last year.

The regime’s immediate goal is retaking full control of the M4 and M5 highways, which link Damascus to the former economic centre of Aleppo and the country’s east to west. Syrian and Russian airstrikes on hospitals, markets and bakeries have killed 300 civilians and emptied towns of residents. Over the last two weeks ground troops have surged forward, capturing dozens of deserted towns and villages.

Facebook Twitter Pinterest Turkish military vehicles at the Syrian-Turkish border on Sunday. Photograph: Khalil Ashawi/Reuters

Many of the 700,000 people who have fled the violence had already been displaced from home numerous times as the regime has clawed back territory from rebels over the course of the war.

Turkey, which already hosts around four million refugees, fears a fresh influx from Syria and has kept its border closed to the newly displaced people in Idlib.

Convoys of families with mattresses stacked on trucks have been criss-crossing the war-torn province in the exodus, which has coincided with a bitter winter.

Camps and settlements are full and even unfinished buildings, schools and mosques are now overcrowded. Snowfall in some regions and sub-zero temperatures now risk a humanitarian catastrophe, prompting the UN to make an urgent appeal for shelter solutions.