ISTANBUL (Reuters) - 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.
The Syrian army denies its strikes target civilians and says its forces only bomb militants associated with hardline Sunni fundamentalist groups linked to al Qaeda.
Turkey's Cavusoglu, who earlier on Tuesday met the chief negotiator for the Syrian opposition, said in his tweet on Tuesday that the sides were close to agreement on forming a U.N.-sponsored committee to draft a new Syrian constitution.
In December, Russia, Iran and Turkey failed to agree on the makeup of the constitutional committee, but negotiations have continued since then.
(Reporting by Sarah Dadouch and Daren Butler and Suleiman al Khalidi in Amman; Editing by Jonathan Spicer, William Maclean and Frances Kerry)