The presidents of Turkey and Russia spoke over the phone on Friday, a day after Syrian government airstrikes killed 33 Turkish troops, significantly ratcheting up tensions between Ankara and Moscow.
It was the highest number of Turkish soldiers killed in a single day since Ankara first intervened in the Syrian conflict in 2016.
The development was the most serious escalation in the conflict between Turkish and Russia-backed Syrian forces and raised the prospect of all-out war with millions of Syrian civilians trapped in the middle.
NATO envoys held emergency talks at the request of Turkey, a NATO member, and scores of migrants began converging on Turkey's border with Greece seeking entry into Europe after Turkey said it was no longer able to hold refugees.
Turkish President Recep Tayyip Erdogan, whose country already hosts more than 3.5 million Syrian refugees, has long threatened to open the gates for millions of refugees eager to flee to Europe unless more international support was provided.
Turkish Foreign Ministry spokesman Hami Aksoy warned the movement of migrants to the West could continue if the situation in Idlib deteriorated.
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Some asylum seekers and migrants in our country, worried about developments, have begun to move towards our western borders, he said.
If the situation worsens this risk will continue to increase. However, he added that there was no change in Turkey's migration policy.
Refugees, meanwhile, headed to the land border with Greece, taking minibuses and taxis from Istanbul.
Dozens waited at the Turkish side of the border gate at Pazarkule. Others headed to Turkey's west coast to attempt to reach the Greek islands lying a short distance away.
Turkish NTV showed around 20 people clambering aboard a rubber dinghy at Ayvacik, northwest Turkey, in broad daylight on Friday and setting off for the island of Lesbos.
A Greek police official said dozens of people had gathered on the Turkish side of the land border in Greece's northeastern Evros region, shouting open the borders.
Greek police and military border patrols were deployed on the Greek side to prevent anyone trying to cross without authorization.
The official spoke on condition of anonymity as they were not authorized to speak to the press on the record.
The latest crisis stems from a Russian-backed Syrian government military campaign to retake Syria's Idlib province, which is the last opposition-held stronghold in Syria.
The offensive, which began December 1, has triggered the largest single wave of displacement in Syria's nine-year war, sending nearly 950,000 people fleeing to areas near the Turkish border for safety.
Ankara, the Syrian rebels' last supporter, sealed its borders in 2015 and under a 2016 deal with the European Union agreed to step up efforts to halt the flow of refugees.
Turkey has had 54 soldiers killed in Syria's northwestern Idlib province since the beginning of February, including the latest fatalities, and feels the need to respond strongly.
Turkey's DHA news agency reported Friday that some 300 Syrians, Iranians, Iraqis, Moroccans and Pakistanis were gathering at the border with Greece, while others massed at beaches facing Greek islands off Turkey's western coast.
Omer Celik, spokesman for Erdogan's ruling party, said Turkey was no longer able to hold refugees following the Syrian attack reiterating a standing threat by Ankara.
The Thursday night attack in Idlib sharply raises the risk of direct military confrontation between Turkey and Russia, although Turkish officials blamed Syria, not Russia, for the attack.
The Turkish stock market fell 10 per cent in the wake of the airstrike, while the Turkish lira slid against the dollar.
Rhami Dogan, the governor of Turkey's Hatay province bordering Syria's Idlib region, said in addition to the 33 soldiers killed, 32 troops wounded in the attack were being treated in hospitals.
Turkey is a main backer of the Syrian opposition while Russia has been giving military support to the weeks-long Syrian government offensive in Idlib.
The Kremlin said Erdogan and Russian President Vladimir Putin discussed implementing agreements in Idlib.
Russian Foreign Minister Sergei Lavrov, speaking in Luxembourg, said Russia remains committed to the agreements reached by Putin and his Turkish counterpart.
Commenting on the deaths of the Turkish troops in Idlib on Thursday, the minister said that if the agreements between the two countries' armies "including sharing of accurate coordinates of the Turkish troops' location" had been implemented in full, such tragedies could have been avoided.
Russia's Defense Ministry said the Turkish troops that came under fire in Idlib were deployed among terrorist battle formations.
They were in the area of Behun, and according to coordinates given to Russia's Reconciliation Center in Syria, "there were no Turkish military units in the area ... and there weren't supposed to be, the ministry said, Russian air forces did not carry out airstrikes in the area, the statement added, and after receiving information about Turkish casualties, the Russian side took all the necessary measures in order for the Syrian forces to stop the fire.
Meanwhile, two Russian frigates carrying cruise missiles have been deployed to Syria, Russian navy officials said Friday.