Greece said on Sunday it has blocked nearly 10,000 migrants at its border with Turkey.
Turkey on Sunday announced the launch of an offensive against the Moscow-backed Syrian regime, as Ankara put pressure on Europe by opening its border for migrants to seek passage to the continent via Greece.
Tensions have soared between Russia and Turkey - who back opposing forces in the Syria's civil war - after an airstrike blamed on Damascus killed dozens of Turkish soldiers in Idlib last week.
Turkish and Syrian military exchanged fire over the weekend with Syrian forces targetting a Turkish drone and artillery and Ankara claiming to have shot down two Syrian fighter jets.
The situation in rebel-held Idlib was already volatile as the regime supported by Russian air power pressed an assault on the region, killing hundreds of civilians, in a bid to retake the last opposition enclave in an eight-year civil war.
The confrontation between the Russia-backed Syrian military and Nato-member Turkey, which supports Syrian rebels, has prompted worries over a wider conflict and a migrant crisis in Europe similar to 2015.
Migrant numbers have already surged along the rugged frontier after Turkey's President Recep Tayyip Erdogan, seeking to pressure the EU over Syria, said the country had "opened the doors" to Europe.
Greece said Sunday it has blocked nearly 10,000 migrants at its border with Turkey.
As migrant boats continued to land on Greek islands, Turkish Defence Minister Hulusi Akar announced the first confirmation of a full and continuing operation against Damascus.
"Following the heinous attack on February 27 in Idlib, operation 'Spring Shield' successfully continues," Akar said in a video shared by the defence ministry.
Turkish forces hit Syrian regime positions after Erdogan warned Damascus would "pay a price" for the air strike that killed 34 Turkish troops inside Idlib on Thursday.
Under a 2018 deal with Russia meant to bring calm to Idlib, Turkey has 12 observation posts in Syria - but several have come under fire from Syrian President Bashar al-Assad's forces.
Turkey on Friday said it retaliated by hitting more than 200 Syria regime targets in drone and artillery bombardments.
Turkey wants the international community to establish a no-fly zone over Idlib, where Islamist fighters backed by Ankara pose the biggest obstacle to Damascus seizing back control over all of Syria.
Planes shot down
Syrian state media reported that Turkey targeted two regime planes over Idlib.
Sana also reported the regime shot down a Turkish drone near the town of Saraqeb, publishing footage of an aircraft tumbling from the sky in flames. That could not be immediately confirmed.
The Turkish defence ministry confirmed one of its drones was shot down and two other anti-aircraft systems had been destroyed.
It added two SU-24 regime planes that were attacking Turkish aircraft were downed.
The latest violence has raised tensions between Moscow and Ankara, but Ankara insists Turkey did not wish to clash with Russia.
Turkish media reported on Sunday that Erdogan and Russian President Vladimir Putin would meet in Moscow on March 5.
Earlier on Sunday, Istanbul police detained the editor-in-chief of the Turkish version of Russia's Sputnik website as its offices were being searched in Istanbul.
Three of its journalists were also taken to a courthouse in Ankara for questioning, likely related to a Sputnik article in English claiming Turkey's Hatay province was "stolen" from Syria. Colonial power France ceded the southern region to Turkey in 1938.
The news website later said they had been released.
The Russian and Turkish foreign ministers spoke by telephone on Sunday, Moscow's ministry said, to discuss preparations for the meeting between Putin and Erdogan, and the safety of the Sputnik journalists.
Some 13,000 migrants have amassed at the Turkey-Greece border, including families with young children who spent the night in the cold, the International Organization for Migration said.
An estimated additional 2,000 migrants arrived at the Pazarkule border gate Sunday, including Afghans, Syrians and Iraqis, according to an AFP reporter.
But as the crowds rushed to enter Europe, Greek police and soldiers blocked 9,972 "illegal entrances" from entering the northeastern Evros region in the past 24 hours, a Greek government source said.
The UN refugee agency spokesman Babar Baloch called for "calm and easing of tensions on the border," as he urged countries to "refrain from the use of excessive and disproportionate force."
European Commission chief Ursula von der Leyen on Saturday said the EU was watching "with concern" and stood ready to deploy its Frontex border guard agency.
The developments recalled events in 2015 when over a million migrants fled to Europe, mainly via Greece in what became the continent's worst refugee crisis since the Second World War.
The EU's commissioner for migration, Margaritis Schinas, tweeted Sunday he had requested an extraordinary meeting of EU interior ministers to discuss the situation.
Erdogan said Turkey, home to some 3.6 million refugees, did not plan to close the borders because "the (EU) should keep its promises."
He was referring to the 2016 deal with Brussels to stop the flow of refugees in exchange for billions of euros.