Turkey has warned it is "no longer able to hold refugees" after it called an emergency NATO meeting as tensions rose on its border with Syria.
At least 33 Turkish soldiers were killed following an air strike on Thursday from Russian-backed Syrian forces, the biggest number of Turks killed in a single day since the country first intervened in 2016.
Russia's Defence Ministry said the troops had come under fire in Idlib were deployed among "terrorist battle formations", and claimed they "weren't supposed to be (there)."
Idlib is the final stronghold of fighters opposed to Syrian President Bashar al-Assad, some of whom are supported by Turkey.
Russia's President Vladimir Putin and Turkish President Recep Erdogan spoke on the phone on Friday in an attempt to defuse tensions, the Kremlin said.
The Turkish Defence Ministry released video on Friday showing retaliatory strikes on Syrian government positions.
How have refugees reacted to the escalation?
Many have fled to the closed Turkish border, which already hosts huge makeshifts 'tent cities' of displaced Syrians - unable to go home, and unable to cross over.
Meanwhile, hundreds of migrants gathered at Turkey's borders with Greece, and Greek officials told AP some were shouting "open the borders".
Greek police and military border patrols were deployed on the Greek side to prevent anyone crossing without authorisation. Bulgaria has also bolstered security on its borders.
Turkey already hosts more than 3 million displaced Syrians and pledged in a 2016 deal with the European Union to halt the flow of refugees to Europe.
But since then Turkish President Recep Erdogan has repeatedly threatened to "open the gates" after several disputes with European states, and has now called NATO members together to discuss the rising tensions in Syria.
Atmed, Syria's largest 'tent city', on the closed border with Turkey where about one million displaced Syrians live.
Can NATO - including the UK - get involved?
NATO Secretary-General Jens Stoltenberg said Friday's meeting was held under Article 4 of NATO's founding treaty, which allows any ally to request consultations if it feels its security to be threatened.
He said NATO "expressed their full solidarity with Turkey" and condemned the strike on Turkish soldiers.
"This dangerous situation must be de-escalated... to avoid further worsening of the horrendous humanitarian situation in the region and to allow urgent humanitarian access for those trapped in Idlib," he said.
NATO Secretary-General Jens Stoltenberg says Turkey has the "full solidarity" of NATO.
NATO plays no direct role in the Syrian conflict, and Turkey's invasion of the north of the country has come close to sparking a crisis in the military alliance.
France has tried to launch a debate about what would happen should Turkey invoke Article 5 - which requires allies to come to the defence of another member under attack - but such a discussion has not happened.
Turkey's role in the Syrian conflict
Turkey has had 54 soldiers killed in Syria’s northwestern Idlib province since the beginning of February, including the latest fatalities.
In recent weeks it has sent thousands of troops to Idlib, as well as tanks and other equipment.
On Wednesday, Erdogan gave the Syrian government until the end of February to pull back from their recent advances or face more Turkish "intervention".
Thursday's air strikes came as Turkish-backed opposition forces took a strategic northwestern town from Assad's forces, cutting off a key Syrian highway just days after the government reopened it.
At home, Erdogan's party's head official Devlet Bahceli said the situation in Idlib "threatens our national survival".