Turkey has warned it will not stand by and watch a Russian-led attack on Syria’s Idlib province, which it said could turn the densely-packed north west of the country into a “lake of blood” and force an overwhelming exodus of refugees.

Speaking hours after a three-way summit in Tehran at which the Turkish president, Recep Tayyip Erdoğan, pleaded with Russia and Iran to halt any forthcoming offensive, Erdoğan ramped up his rhetoric, insisting Ankara would not participate in “furthering the interests of Bashar al-Assad”.

Vladimir Putin had earlier rejected Erdoğan’s calls for a ceasefire in Idlib, the last opposition stronghold in Syria. The Russian president holds the key to the forthcoming operation – the most significant in a series of Russian and Iranian-led victories across the country.

“We will neither watch from the sidelines nor participate in such a game,” Erdoğan said in a message on Twitter. Turkish government spokesman Ibrahim Kalin said on Saturday: “Idlib is a ticking bomb. We can turn it off and start a new process in Syria if the international community gets serious about the Syrian war and shows that they do care about the Syrian people.” Meanwhile, Russian jets renewed their bombardment of southern Idlib, intensively attacking the city of al-Habit, killing four people. Russian jets also struck in the east of the province.

After seven years of war, Idlib has become the focus of a struggle that has spilled well beyond Syria’s borders, transforming the conflict into one of the most complex and consequential battlefields of modern times.

At the heart of global concerns are an estimated 3 million people crammed into Idlib and its surrounds, at least half of whom have fled vanquished opposition areas. The UN has raised the possibility of humanitarian corridors being opened into areas controlled by Damascus. However, many of those now besieged in Idlib say they are not willing, even under bombardment, to risk crossing into government-run areas.

“The problem is not only Russian and regime jets hovering about,” said Omar, 53, a barber in the province. “The problem is that the Assad regime will eradicate all the civilians who will attempt to go through humanitarian corridors; if they’re not murdered they’ll be sent to jail. Civilians are more scared of regime prisons than getting bombed. What you people call humanitarian corridors we call corridors of death and torture. Those who are rooting for corridors are rooting for slow deaths.”

While the scale of the expected exodus concerns Turkish officials, Ankara is also deeply worried about the implications for its interests in the aftermath of Assad being able to claim a decisive victory just south of the Turkish border. As war has ravaged northern Syria, Turkey has taking an ever more visible stake, carving out a zone of influence that it uses as a buffer both against multiple sides in the conflict – but especially the Kurds.

Turkey had armed and supported various incarnations of the Free Syria Army, an amorphous group of anti- Assad fighters who have lately coalesced into an alliance known as the Northern Front. Turkey had helped raise and train groups within the organisation to fight Assad, but earlier this year co-opted them to oust Kurdish forces from Afrin, just south of its border.

That victory mean Kurds were pushed back from the frontier with Syria, from west of the Euphrates river, giving Turkey more leverage to shape its interests. Renewed chaos in Idlib could potentially jeopardise such gains, and draw its proxies into the crosshairs of the Russian air force, which played decisive roles in the battles for east Aleppo and eastern Ghouta, both of which have been returned to regime control.

Turkey has positioned some of its own forces in 12 small bases in Syria, to safeguard its interests and make it notionally more difficult for a full-scale attack to be launched. “Russian jet fighters and the regime ground forces cannot afford attacks while Turkish soldiers are there,” Kalin said. “We know that they do not care about civilians and legitimate, moderate opposition forces.”

Russia has demanded that Erdoğan force the withdrawal of jihadist forces from Idlib, a role Ankara said it could not play. Jihadists are mixed within opposition units in the province and have held sway within a large opposition alliance known as Tahrir al-Sham. Putin said in Tehran on Friday that an offensive would be launched imminently if jihadist groups failed to leave.

Kalin warned of a renewed exodus to Europe if attack orders were given. “Any attack on this province of 3.5 million people … will trigger another wave of migration into Turkey and from there to Europe and elsewhere,” he said. Turkey has largely completed a wall along its 500-mile border with Syria, meaning people trying to flee would face a much more difficult task than in 2012-15, when up to 3 million refugees made their way to Europe.

Abu Mukhtar, an unemployed 48-year-old Idlib resident, said the Tehran summit had temporarily calmed nerves. “It’s not so bad at the moment,” he said. “People are feeling a bit more relieved after the Turkish-Iranian-Russian truce. But the people around me here are having no talks of humanitarian corridors and fleeing. Who believes a Russian anyway?”