ISTANBUL   -   Turkish Defense Minister Hulusi Akar and his Russian counterpart discussed ways to reduce tension in Syria’s Idlib province, the Turkish Defense Minis­try said on Tuesday, after the biggest military escalation in northwest Syria in nearly a year.

Russia has backed the government of Syrian President Bashar al-Assad, while Turkey has backed some rebels in Syr­ia’s eight-year civil war, but they have re­cently worked together to try to contain fighting in the country’s northwest. That effort has been strained by the surge in violence in Syria’s last major insurgent stronghold in recent weeks.

The offensive by the Syrian army and its allies, backed by Russia, has uprooted more than 150,000 people, the United Nations says, while rescue workers and civil defense officials say more than 120 civilians have been killed.

Turkish Foreign Minister Mevlut Ca­vusoglu called the attacks by Syrian forces a flagrant violation of a Septem­ber ceasefire that had averted a govern­ment offensive. He said in a tweet on Tuesday it went counter to the spirit of Turkey’s efforts to work with Russia and Iran to reduce hostilities and casualties in Idlib and neighboring areas.

On Monday, rebels said they mounted a counterattack against government forces. A senior rebel commander said on Tuesday the offensive showed an ar­ray of rebel forces - from Turkey-backed rebels to jihadists - were still able to prevent the army from making major advances despite heavy air strikes.

“We conducted this lighting offensive to show the Russians we are not easy prey and throw the regime off balance,” said Abu Mujahid, from the Turkey-backed National Liberation Front.

Turkish President Tayyip Erdogan told his Russian counterpart, Vladimir Putin, on Monday that the Syrian gov­ernment was targeting Turkish-Russian cooperation in Idlib by violating the September ceasefire.

A senior opposition figure in touch with Turkish intelligence said the rebels’ ability to withstand some of the heaviest air strikes in over a year had strength­ened Ankara’s hand in recent days.

“We were told that Erdogan told Putin the deal would collapse if mat­ters escalated much more beyond this,” said the opposition figure who requested anonymity because of the sensitivity of the matter.

Moscow had been piling pressure on Ankara to start an operation against the opposition-held areas after Turkey’s failure to push rebels to agree to Rus­sian patrols and get al Qaeda-inspired militants out of a buffer zone that un­derpinned the Turkish-Russian deal.

Since April 28, a total of 18 health fa­cilities have been struck, the U.N. Office for the Coordination of Humanitarian Affairs (OCHA) told Reuters on Monday. Two hospitals were hit twice.