Renewed bombardment in north-west Syria that has displaced 200,000 people and destroyed 12 healthcare centres could have been sparked by Russia and Turkish moves to entrench their zones of influence as the seven-year conflict winds down, according to regional diplomats.

The bombardment in Idlib province began two weeks ago and has intensified in recent days, prompting rescue workers to describe an “unprecedented humanitarian catastrophe”.

The violence has sparked fears of a final, devastating, showdown in the most densely packed corner of Syria – the last part of the country to remain outside regime control.

Syria conflict: why does Idlib matter and what could happen? Read more

Hospitals and clinics in the southern end of Idlib and northern edge of neighbouring Hama province have been systematically attacked by Russian warplanes, observers on the ground and monitoring groups have confirmed. The blitz has raised the spectre of a long-anticipated ground attack on the province, where a cornered population of at least 3 million people has nowhere left to run.

However, two senior diplomats believe such a scenario is less likely than a limited campaign that gives Russian and Syrian forces a foothold in Idlib, in return for allowing Turkey to deepen its current zone of control further to the east.

The British foreign secretary, Jeremy Hunt, condemned the “flagrant violation” of the ceasefire agreement by Russia and the Syrian regime, which has also forced 150,000 people from their homes and had reportedly left a dozen children dead.

Hunt said the attacks included the use of barrel bombs “for the first time in seven months” and threatened a “swift and appropriate response” if Syria used illegal chemical weapons.

Since the Syrian conflict erupted in 2011, Syrian president Bashar al-Assad’s backers have played an increasingly decisive role in shaping the outcome. And with battlefields subdued elsewhere in the country, intention has shifted to Idlib.

The Russian president, Vladimir Putin, and his Turkish counterpart, Recep Tayyip Erdoğan, agreed last September that Moscow and Ankara would jointly oversee a nine-mile demilitarized zone between rebel and regime lines intended to keep the two sides apart. That agreement had been the centrepiece of a de-escalation pact that had kept the province relatively stable until mid-April.

Its apparent collapse has drawn little criticism from Ankara, which had strongly backed elements of the anti-Assad opposition in Idlib and has taken a stake inside northern Syria to safeguard its own interests. “There are suggestions of an arrangement between Russia and Turkey and the regime which would eat into the buffer zone by up to 25 miles in exchange for the Turks being able to take Tel Rifaat,” said one diplomat.

The small Kurdish controlled town of Tel Rifaat in northern Syria has long been a target of Turkey’s military, which ousted Kurdish militants from the neighbouring town of Afrin early last year.

On Sunday, Turkey’s vice president, Fuat Oktay, suggested that Tel Riffat was once again in military leaders sights. Responding to an attack, which reportedly killed a Turkish soldier in the area, Oktay said: “The agreement was for us to stop there [Tel Rifaat], but if these attacks continue, this may take a different shape. We are discussing this with Russia.”

“The Turks are in there somewhere,” the diplomat said. “They’re at least aware of what the Russian plans are.

Labib al-Nahhas, a political activist formerly connected to the Syrian armed opposition leadership, said other factors may be driving the assault on Idlib. “The latest offensive by Russia is due to two main reasons,” he said. “They have reached a real bottleneck in the Astana peace process … and realised that the current dynamics will not enable Russia to achieve its vision in Syria.

“The other reason is the fast demise and disintegration of the Assad regime at all levels: political, economic, social, army and recently even security. Russia knows that the window of opportunity to make sustainable gains in Syria is closing down, and they needed to cover up the regime’s current situation by launching this attack and hoping to achieve a victory that would shake things up in their favour.

Chris Allbritton, communications director of Refugees International, said: “It is difficult to overstate the urgency of this looming humanitarian disaster if nothing is done to protect these people who often have lost everything.

“Idlib is the last refuge for Syrians who were forced to flee conflict in other parts of the country; its pre-war population of 1.5 million has doubled to 3 million people, and two-thirds of them depend on humanitarian aid just to survive.”

Majd Khalaf, a liaison officer with the White Helmets, which have responded to attacks in opposition areas through much of the war, said: “There is an unprecedented humanitarian catastrophe going on in Idlib. The attacks targeting hospitals, clinics and trauma centres leaves us with no choice with the wounded and injured civilians, but to take them far to the north of Idlib which is a long road, and on the way, the Syrian army helicopters are attacking our ambulances.

“There is a difference in this campaign by the Russians, and the Assad regime. They are committed to erasing every sign of life in the area. In the past, an assault like this was followed by talks that resulted in agreements, but this is a new brutality.”

Additional reporting by Muhammad Rasool

• This article was amended on 9 May 2019. A reference to Russia or Turkey using chemical weapons should have been to Syria.