The assault by Bashar al-Assad’s regime on the last Syrian province under rebel control could spark a “new wave of migration”, a top Turkish official has warned, amid growing alarm over a campaign that has displaced more than 100,000 people.

The fighting in Idlib, which has intensified in recent days amid rebel counterattacks, has raised fears of a humanitarian catastrophe in an area already crowded with refugees. “This displacement is the biggest perhaps in the Syrian revolution since its beginning until today,” said Mounir Mustafa, the deputy chief of the civil defence rescue workers organisation known as the White Helmets.

Tens of thousands of people have fled from the frontlines in Idlib, which until recently has been the only province almost wholly controlled by rebels fighting to overthrow the government in Damascus. According to the UN, in the past week 30,000 refugees have moved into Idlib’s heavily populated cities as well as along the Turkish border, crowding into existing camps in the harsh winter cold. Local authorities say the figure is far higher.

The intensified attacks in Idlib will … cause new suffering Binali Yildirim

“The intensified attacks in Idlib will trigger a new wave of migration and cause new suffering,” the Turkish prime minister, Binali Yildirim, said in comments carried by the state-run Anadolu Agency. His warning will alarm EU member states, whose deal with Ankara to stem the flow of refugees and migrants across the Aegean Sea has reduced the numbers attempting the journey from Turkey. Many of those fleeing the new Assad advance subsisted by raising livestock in southern Idlib and northern Hama, and their flight north has left them without a livelihood. The International Rescue Committee (IRC), which is assisting some of the newest refugees, said that two-thirds of them were living in makeshift tents, with up to three families in each, and that many of the sites do not have toilets.

Facebook Twitter Pinterest An airstrike on Kafr Battikh village in Idlib province killed 14 people on 13 January. Photograph: Anadolu Agency/Getty Images

“We are extremely concerned for the safety of the 2.6 million people living in Idlib if the frontline continues to advance,” said Thomas Garofalo, an IRC Middle East official. “People have told us that they will have no choice but to uproot themselves once again and head further north. They will be heading to displacement camps that are already far beyond capacity, which means their situation will get even worse, in the dead of a wet, cold winter.”

Zeid Ra’ad al-Hussein, UN high commissioner for human rights, said Assad’s offensive was “jeopardising the safety of hundreds of thousands of civilians”.

The bombing is constant. It’s not daily but hourly, on the whole region, and it seems to be completely random Rescue worker, White Helmets

In the spring of 2015 a coalition of mostly Islamist rebels, including the then al-Qaida affiliate Jabhat al-Nusra, swept through Idlib, ousting government loyalists. Since then the region has endured relentless bombardment, including reported attacks with chlorine gas and sarin. Refugees from other parts of Syria have also swelled Idlib’s population to more than two million, moving there after rebel surrender deals.

Hay’at Tahrir al-Sham, an alliance formed by the merger of Jabhat al-Nusra with smaller Islamist groups, enjoys military predominance in the province. Its hardline edicts have elicited protests from other residents who also oppose the Assad government. Aid workers are worried that the Syrian army will use the group’s presence in Idlib as a pretext for bombing the increasingly crowded civilian centres. Dozens have already been killed in the aerial bombardment and shelling.

“The bombing is constant. It’s not daily but hourly, on the whole region, and it seems to be completely random,” said Mustafa al-Haj Youssef, a rescue worker for the White Helmets in charge of Idlib. “The thing that hurts us most is the double-tap strikes, when the regime bombs an area, and we go to it after receiving emergency calls, and then they bomb it again. The displacement [of refugees] is usually out of fear of indiscriminate bombing,” he said.

The Assad regime’s advance appears aimed at securing a foothold in the province, with an ongoing drive towards the Abu al-Dhuhour military complex. But that surge, after days of initial gains, is being met with stiff resistance in a rebel counterattack and there are reports of continuing fierce combat.

The launch of this ground campaign is a blow to the rebels, who appeared within range of overall victory against a teetering Assad when they conquered Idlib. But the decisive intervention of Russia, along with Iranian-backed Shia militias, has given Assad the military momentum, and he has pressed his advantage in an effort to scupper peace negotiations and secure a victory free of concessions.

The regime’s campaign has been coupled with a renewed attack on hospitals, at least eight of which have been targeted in Idlib in recent weeks. Villages have been abandoned wholesale near the frontline.

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The violence has cast doubt on efforts to negotiate a Syrian peace settlement brokered by Russia, Turkey and Iran. A new deal had designated Idlib and other regions of Syria as “de-escalation zones” to stem the violence and create the conditions for talks.

Moscow had set late January as the time for a national dialogue conference, to be held in Sochi, Russia. But Turkish officials have said that the bombardment in Idlib is endangering those talks, and summoned the Russian and Iranian ambassadors to express their concerns.

“The Syrian people have lost all confidence in the international community, and do not believe anyone can stop this killing of Syrians,” the White Helmets’ Mustafa said.

“But we are hoping the aid organisations will assume their responsibilities and provide whatever help is necessary to those people who are being forced to leave their homes for other areas as a result of the bombardment.”