UN chief Antonio Guterres on Friday described an increase in fighting in northwest Syria that Martyred dozens of Turkish troops as “one of the most alarming moments” of the nine-year-old war and – along with most UN Security Council members – called for a ceasefire.

The 15-member Security Council met on Friday after 33 Turkish soldiers were martyred in Idlib, one of the deadliest attack suffered by Turkey’s army in nearly 30 years.

“We call for the Russian Federation to immediately ground its warplanes and we call for all Syrian forces and their Russian backers to withdraw to the ceasefire lines first established in 2018,” U.S. Ambassador to the United Nations, Kelly Craft, told the council.

Turkey and Russia gave opposing accounts to the Security Council of what happened.

Russia’s UN Ambassador Vassily Nebenzia said Turkish troops shared coordinates with Russia, which were then given to Syrian government forces, to avoid conflict on the ground. He said Russian warplanes were not providing support in the area where the Turkish soldiers were targeted.

Turkish U.N. Ambassador Feridun Sinirlioglu disputed Nebenzia’s account, saying that “radar tracks” showed that Syrian government and Russian aircraft were flying in formation during the time of the attack.

“We had prior coordination in writing with Russian forces about the location of our convey and air strikes continued despite our immediate warnings right after the very first attack,” he said.

Craft urged Guterres to do everything in his power to broker a ceasefire, saying “the U.N. must play a central active role if we are to avoid even greater escalation.”

Ahead of the Security Council meeting, Guterres called for an immediate ceasefire “before the situation gets entirely out of control,” adding that: “Civilians are paying the gravest price … And the noose keeps tightening, as the frontlines reach more densely populated areas.”