Opening the frontier could unleash a repeat of the migration crisis of 2015-2016, when more than a million people arrived by sea in Greece and crossed the Balkans on foot, until Turkey shut its frontier in a deal with the EU, according to Reuters.

By the early hours of Friday, refugees and migrants were already making their way to frontier posts. The official said police and border guards had been told to stand down and allow exit by both land and sea.

One column of migrants made their way towards the frontier on foot in the early morning light, with one man carrying a small child in his arms. Others headed there 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 on the outskirts of Istanbul.

“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 west of Istanbul.

A million civilians have been displaced since December inside Syria near the Turkish border in desperate winter conditions, perhaps the worst humanitarian crisis of the nine-year war. Turkey is already home to 3.7 million Syrian refugees and 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.

Ankara’s fury over Thursday’s attack — the deadliest suffered by the Turkish army in nearly 30 years — raised the prospect that President Tayyip Erdogan will launch a full-scale operation against the Russian-backed Syrian army.

Russia said Erdogan discussed the crisis by phone on Friday with President Vladimir Putin.

“We have decided, effectively immediately, not to stop Syrian refugees from reaching Europe by land or sea,” said the official, who requested anonymity. “All refugees, including Syrians, are now welcome to cross into the European Union.”

Reporter’s code: 50101