The collapse of the Isis caliphate’s last stronghold in Syria is sending shockwaves across the region, changing the calculations of the major powers as they jockey for advantage. Triumphalism in Washington, Moscow and Damascus risks obscuring the human cost of a “victory” that may quickly prove transitory.

Of immediate concern is the fate of civilians, mainly women and children, displaced from formerly Isis-controlled areas where many were held against their will. The independent International Rescue Committee says up to 4,000 people are fleeing towards the al-Hawl refugee camp in north-east Syria.

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“Most have suffered four years under the horrors of Isis and are now arriving at al-Hawl extremely hungry and dehydrated. Many have also incurred life-changing wounds. There are numerous reports of violence against women and girls and families being separated on the journey,” the IRC said.

Also of urgent concern is what will be done with captured Isis jihadists. So-called “foreign fighters” and their supporters may seek to return to their countries of origin, confronting Britain and other governments with awkward choices.

But fears are growing that large numbers of Syrian Isis fighters may move to Idlib Province in north-west Syria, the last big populated area not controlled by Bashar al-Assad’s regime. In the past two years Idlib has become a haven of last resort for retreating rebels and militant Islamists. It is also home to 3 million Syrian civilians, half of whom are internally displaced.

“Distributing Syrian fighters among civilians in Idlib will mean the truth they hold about those they killed, kidnapped and disappeared will never be revealed. These fighters must be brought before courts to reveal what they know about the atrocities Isis committed,” said Laila Kiki of the Syria Campaign, a human rights group. “There is still a huge number of people unaccounted for. According to the Syrian Network for Human Rights, 8,349 people have been detained and forcibly disappeared by Isis in all its territories.”

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The transfer of Isis fighters would also complicate efforts to suppress the al-Qaida affiliate, Hayat Tahrir al-Sham, that now controls most of Idlib. Activists say it could give Assad’s Russian and Iranian-backed forces a long-sought excuse to launch an offensive to retake the province, potentially triggering a mass refugee exodus north into Turkey.

Turkey’s desire to prevent this outcome tempered celebrations in Sochi last week when Assad’s main backers met to discuss fallout from the caliphate’s defeat. Exploiting the moment with support from Hassan Rouhani, Iran’s president, Vladimir Putin demanded “concrete steps … to completely destroy this hotbed of terrorists [in Idlib]”. But Recep Tayyip Erdoğan, Turkey’s president, has blocked a new military operation there, for now at least. Erdoğan’s focus lies elsewhere, on the borderlands of north-east Syria controlled by US-allied Kurdish forces, whom he regards as mortal enemies. The Isis rout has increased the chances of a Turkish military intervention similar to last year’s invasion of Afrin. Erdoğan wants to create “safe zones” inside Syria to push back the Kurds and supposedly secure his southern border.

Assad, supported by Russia, wants, in contrast, to reassert sovereign control over all Syrian territory, including that vacated by Isis. But Erdoğan cares little. The main reason he has not already acted is Donald Trump. Against the advice of his generals and Nato allies, Trump has ordered US forces in Syria to leave by the spring. When they quit, Erdoğan will make his next move.

The Isis collapse carries dire implications for Iraq, too. The Iraqi army, with international help, drove the jihadists out of Mosul and other cities in 2017. But they are now regrouping in Sunni areas and could soon pose a dangerous new threat, according to a Pentagon report published last month. “Isis is regenerating key functions and capabilities more quickly in Iraq than in Syria,” the report said., underscoring the case for continued counter-terrorism operations in both countries. “Absent sustained pressure, Isis could likely resurge in Syria within six to 12 months and regain limited territory in the [middle Euphrates river valley].”

Iraq’s Shia leaders are meanwhile alarmed at Trump’s suggestion that US troops freed up in Syria could be redeployed in Iraq, not to prevent an Isis comeback but to “keep watch” on Iran. “Don’t overburden Iraq with your own issues … We live here,” Barham Salih, Iraq’s president, told Trump. Iraq’s pro-Iran Hizbullah Brigades warned the plan could make “American forces legitimate targets for the Iraqi resistance”.

The idea that Iraq could be used as a launchpad for a new American war of choice, this time against Iran, worries Democrats in Washington, and European governments. They prefer to keep the focus on fighting jihadist terrorism, and think Trump risks dropping the ball. Iran, meanwhile, has bigger fish to fry, notably confronting Israel in western Syria, and Saudi Arabia in Yemen. Tehran fears covert American regime change, destabilisation and sabotage plots more than it fears Isis. “The Americans must leave Syria,” Ali Akbar Velayati, a senior adviser to Iran’s supreme leader, said this month – and preferably get out of the Middle East altogether.