Groups of migrants in Turkey headed toward its borders with Greece and Bulgaria on Friday, Reuters reporters said, after a senior official said Ankara will no longer abide by a 2016 EU deal and stop refugees from reaching Europe.
Late on Thursday, Turkey said 33 Turkish soldiers were killed in an air strike by Syrian government forces in Syria's northwestern Idlib region.
The official then told Reuters that Turkish police, coastguard and border security officials had been ordered to stand down on refugees' land and sea crossings towards Europe in anticipation of the imminent arrival of refugees from Idlib.
"We heard about it on the television," said Afghan migrant Sahin Nebizade, 16, one of a group of migrants packed into one of three taxis that were 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 (124 miles) west of Istanbul.
Turkey already hosts some 3.7 million Syrian refugees and has repeated that it cannot handle more. Under a 2016 deal, the European Union has provided billions of euros in aid in return for Ankara agreeing to stem the influx of migrants into Europe.
The burden of hosting refugees "is too heavy for any single country to carry", the Turkish official told Reuters.
Pro-government Demiroren news agency said there were around 300 migrants, including women and children, in one group which arrived in Edirne overnight and headed for the borders with the two EU countries Bulgaria and Greece.
Syrians, Iranians, Iraqis, Pakistanis and Moroccans were among those in the group, it said.
Reuters saw migrants gather on Friday on the western Turkish coastal district of Ayvacik in Canakkale province with the aim of traveling by boat to Greece's Lesbos island.
Turkish President Tayyip Erdogan has repeatedly threatened to "open the gates" for migrants to travel to Europe. Doing so now could draw Western powers into the standoff over Idlib.
Some one million civilians have been displaced in Syria near Turkey since December as Russian-backed Syrian government forces seized territory from Turkish-backed Syrian rebels, creating the worst humanitarian crisis in the nine-year war.
Broadcaster NTV showed scores of people walking through fields wearing backpacks and said they had tried to cross the Kapikule border into Bulgaria, but were not allowed through.
It said the same group of migrants had then walked through fields to reach the Pazarkule border crossing into Greece, but it was unclear what happened to them thereafter.