ANKARA/ISTANBUL (Reuters) - Refugees in Turkey headed towards European frontiers on Friday after an official declared that borders had been thrown open in response to the escalating war in Syria, a day after 33 Turkish soldiers were killed by Russian-backed Syrian government troops. European officials rushed to respond to a direct threat to reverse an agreement with Turkey that halted the migration crisis of 2015-2016, when more than a million people arrived by sea in Greece and crossed the Balkans on foot. Moscow and Ankara traded blame over the strike in northwest Syria, the deadliest attack suffered by the Turkish army in nearly 30 years. Turkish financial markets plunged over the prospect of the country being plunged far more deeply into a new escalation of the nine-year-old war across the border in Syria. “We have decided, effectively 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 stood 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 one of three taxis parked on a highway. “We’ve been living in Istanbul. We want to go to Edirne and then on to Greece,” Nebizade said before the taxis headed for the northwestern province of Edirne and border crossings with Bulgaria and Greece, 200 km (124 miles) west of Istanbul. Greece and Bulgaria said they were immediately reinforcing their frontiers. 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. However, both the EU and the United Nations refugee agency noted that reports of any change at the border were still unofficial and Ankara had not made any formal announcement. A MILLION PEOPLE DISPLACED Syria’s civil war has worsened dramatically in recent months despite largely vanishing from the agenda of Western countries. A million civilians have been displaced since December inside Syria near the Turkish border in desperate winter conditions, perhaps the worst humanitarian crisis of a war that has already made half the country homeless. Turkey, already home to 3.7 million Syrian refugees, says it cannot take more. Syrian government forces, backed by Russian air power, have launched an assault to capture the northwest, the last remaining territory held by rebels who are backed by Turkey. With diplomacy sponsored by Ankara and Moscow in tatters, NATO-member Turkey has come closer than ever in the conflict to direct confrontation with Russia on the battlefield. Presidents Tayyip Erdogan and Vladimir Putin spoke by telephone on Friday morning to head off further confrontation. The Kremlin said they agreed on the need for a new arrangement to avert clashes in Syria’s Idlib province. Turkey said the leaders agreed to meet as soon as possible. Ankara’s fury over Thursday’s attack has raised the prospect that Erdogan would launch a full-scale operation against the Russian-backed Syrian army. Since 2016, Europe has relied on Turkey to halt Syrian refugees, while the West has all but abandoned diplomacy to end the war to Moscow and Ankara. The prospect of a new migration crisis caused alarm in European countries already contemplating restrictions on internal borders and public gatherings to fight the coronavirus. “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, announcing the mobilization of extra police on the border with Turkey. “We cannot afford that.” RETALIATION Erdogan has repeatedly threatened to open the gates for migrants to travel to Europe, which would reverse a pledge Turkey made to the EU in 2016 to keep Syrian refugees in return for funding. Turkey, for years the principal ally of rebels fighting against Syrian President Bashar al-Assad, has sent thousands of troops and heavy military hardware in recent weeks into Idlib, where Assad’s forces aim to recapture the country’s last rebel-held bastion and bring the war to a final end. Erdogan has warned that Turkey would repel Assad’s forces unless they pulled back from Turkish observation posts in the region. The United Nations and others have called for an immediate ceasefire, but three rounds of talks between Ankara and Moscow have failed to reach a deal. The air strike on Thursday raised Turkey’s military death toll to 54 in February in Idlib. The governor in Turkey’s border province said 32 other troops were wounded. It was the worst losses suffered by the Turkish military since a 1993 attack by Kurdish separatist guerrillas. Turkey’s defense minister, Hulusi Akar, said the attack occurred despite coordination with Russian officials on the ground and continued even after the alarm was sounded following the first strike. Turkey’s communications director, Fahrettin Altun, said that in retaliation, “all known” Syrian government targets were being fired on by Turkish air and land support units. Russia’s Defence Ministry said the Turkish troops hit by shelling should not have been in that area, and Ankara had not informed Moscow in advance about their location. A senior Russian lawmaker said any full-scale Turkish military operation in Idlib would end badly for Ankara. Turkey’s lira slid to a 17-month low and its main stock index plunged 10% early on Friday even though authorities banned short selling across all Turkish shares. The State Department said the United States was very concerned about the reported attack on Turkish soldiers and stood by “our NATO ally Turkey”.