After the torture and massacre of civilians, after the targeted attacks upon rescuers, doctors and schools, after the barrel bombs and chemical weapons, it should be hard to believe that there could be a new wave of misery for Syria unleashed by Bashar al-Assad and his Russian and Iranian backers. Yet here it is. The assault on Idlib, the last rebel-held enclave, is the largest-scale humanitarian catastrophe of a war now in its ninth year. The United Nations has warned that 832,000 people, most of them children, have been displaced in less than three months; 100,000 people have fled in the past week. Many had already fled the Syrian regime’s murderous assaults before, in some cases three or four times; the province’s population has swelled from 1 million to 3 million since the war broke out. They face sub-zero temperatures, and many don’t even have tents in which to shelter. Doctors report children dying of exposure.

Conditions are likely to worsen. The frontlines are approaching Idlib city, probably sending further waves of families towards the closed Turkish border. Fighting has claimed the lives of both Turkish and Syrian troops, prompting the Turkish president, Recep Tayyip Erdoğan, to move in reinforcements and threaten: “In the event of the tiniest harm to our soldiers … we will hit regime forces in Idlib and anywhere else.”

The 2018 deal brokered by Ankara and Moscow for a de-escalation zone in the province had long been observed as much in the breach as the observance. But Syria claims that it was forced to take decisive action because the extremist militia Hayat Tahrir al-Sham, formerly an al-Qaida affiliate, seized control of the area last year. While it casts its offensive as the eradication of terrorists, its familiar tactics – attacks upon hospitals and bakeries – look more like the deliberate terrorising of civilians than the targeting of jihadist fighters.

Yet a conflict that once transfixed the world in horror is now slipping from its attention. In her award-winning documentary For Sama, the Syrian filmmaker Waad al-Kateab comments of her dispatches from besieged Aleppo: “Millions watched my reports, but no one did anything.” Are they even looking these days?

The Syrian regime has now retaken the critical highway joining the capital, Damascus, to Aleppo. There may now be an operational pause; some hope it may veer away from further clashes with Turkey. But Moscow as well as Damascus seem confident that Mr Erdoğan is bluffing and in the end will fold, feeling forced to protect his relationship with Vladimir Putin rather than engage in an all-out clash, especially given the poor state of his relations with the west.

A Russian delegation to Ankara left earlier this week without signs of progress, and a Turkish delegation was due to arrive in Moscow on Friday. Meanwhile, though Mike Pompeo, the secretary of state, has said that the US stands with its Nato ally Turkey and called for the assault to halt, Robert O’Brien, the national security adviser, asks with barely concealed indifference: “What are we supposed to do to stop them?” Europe has made clear that its overriding interest is ensuring that no refugees reach its shores.

The best-case scenario is a grim one. Even if Damascus halts, the current plight of those fleeing is neither bearable nor sustainable. Turkey already has 4 million refugees; its aim is to return them to a “safe zone” in Syria, not to accept any more by reopening its border. Millions of people in desperate need of supplies and shelter are crammed into this slice of land – “Gaza in Syria”, suggested David Miliband, head of the International Rescue Committee. He described the catastrophe as a symptom of the utter failure of diplomacy, and the international community’s abandonment of Syrian civilians.

As abrupt as the surge in those fleeing has been, this is a long-awaited disaster; the end result of decisions made over years. Only an immediate ceasefire, and the unhindered flow of aid, can offer these desperate civilians any hope of even respite: western powers should be doing everything they can to press for them. This is far less than those now huddled in Idlib are owed – and even this, it seems, may be too much to expect.