Refugees in Turkey headed towards European frontiers on Friday after an official declared that borders had been thrown open, a response to the escalating war in Syria where 33 Turkish soldiers were killed by Russian-backed Syrian government troops.

Moscow and Ankara traded blame over the strike in northwest Syria, the deadliest attack suffered by Turkey’s army in nearly 30 years. The U.N. Security Council called an emergency meeting to avert open conflict between Russia and NATO member Turkey.

Greece and Bulgaria reinforced their borders in response to Turkey’s threat to reopen the frontier, shut under an agreement that halted the migration crisis of 2015-2016, when more than a million people crossed into Europe by foot.

“We have decided, effective immediately, not to stop Syrian refugees from reaching Europe by land or sea,” a senior Turkish official told Reuters on condition of anonymity.

“All refugees, including Syrians, are now welcome to cross into the European Union,” the official said, adding that police and border guards had been told to stand down.

Within hours, a column of dozens of migrants was heading on foot towards the European frontier in the early morning light. A man carried a small child in his arms. Others rode in taxis.

“We heard about it on the television,” said Afghan migrant Sahin Nebizade, 16, in a group packed into taxis on a highway.

At the Pazarkule border post with Greece, scores of migrants faced barbed wire fences and smoke grenades. Some stuck in the no-man’s land between the two countries tried to return to the Turkish side to escape the smoke, only to be turned back.

Hamid Muhammed, who carried a young girl, said he had been turned back by Greek police: “We want the Turkish and European governments to open this gate.”

Greece’s prime minister said no unauthorised crossing would be allowed. Bulgaria’s prime minister said the prospect of a new migration crisis was even more of a threat when European countries were struggling to respond to the coronavirus.

The EU and the United Nations refugee agency noted that reports of a change in Turkish policy at the border were still unofficial and Ankara had not made any formal announcement.

A MILLION DISPLACE

DInside Syria there was ample evidence of the renewed fighting that has brought on perhaps the worst humanitarian crisis of the entire nine-year-old war. A million civilians have been displaced since December inside Syria near the Turkish border in desperate winter conditions. Turkey, already home to 3.7 million Syrian refugees, says it cannot take more.

Reuters journalists at the front line saw huge clouds of white smoke as government forces struck the town of Saraqeb, an important crossroads captured by rebels this week in a rare push-back against the government’s advance.

Rebel fighters sped down highways in pick-up trucks with artillery mounted in the beds. In the provincial capital Idlib, wounded fighters in jeans and camouflage jackets were carried into a clinic on trollies.

Syria’s civil war has worsened dramatically in recent months despite largely vanishing Western countries’ agenda. Government forces, backed by Russian air power, have launched an assault to capture the northwest, the last remaining territory held by rebels backed by Turkey.

With diplomacy sponsored by Ankara and Moscow in tatters, Turkey has come closer than ever to direct confrontation with Russia on the battlefield.

Presidents Tayyip Erdogan and Vladimir Putin spoke by telephone on Friday. The Kremlin said they agreed on the need for a new arrangement to avert clashes. Turkey said the leaders agreed to meet as soon as possible.

“There is a risk of sliding into a major open international military confrontation. It is also causing unbearable humanitarian suffering and putting civilians in danger,” EU foreign policy chief Josep Borrell said on Twitter.

The return of refugees to the frontier was a reminder of Western Europe’s biggest migration since World War Two: the 2015-2016 crisis when 4,000 people drowned trying to reach Greece before Turkey shut the border in return for EU cash.

“At a time when we are imposing stricter border monitoring over the coronavirus, imagine if we have an inflow of hundreds of thousands of migrants,” Bulgaria’s Prime Minister Boyko Borissov said. “We cannot afford that.”Turkey, long the main ally of rebels battling Syrian President Bashar al-Assad’s forces, has recently sent thousands of troops and heavy military hardware into Idlib.

Erdogan has said Turkey will repel Assad’s forces unless they pull back from Turkish posts. The United Nations has urged a ceasefire.

Thursday’s air strike was the worst on Turkey’s military since a 1993 attack by Kurdish separatists.

Turkey’s defence minister said it occurred despite coordination with Russia. Moscow said the Turkish troops should not have been in the area, and Ankara had failed to say where they were.

The United States, which has troops in another part of Syria, expressed solidarity with “our NATO ally Turkey”.