Thousands of migrants and refugees massed at Turkey's western frontier on Sunday, trying to enter Greece by land and sea after Turkey said its borders were open to those hoping to head to Europe.
In Syria, Turkish troops shot down two Syrian warplanes after the Syrian military downed a Turkish drone, a major escalation in the direct conflict between Syrian and Turkish forces.
Turkey's decision to ease border restrictions came amid a Russia-backed Syrian government offensive into Syria's northwestern Idlib province.
That offensive has killed dozens of Turkish troops and led to a surge of nearly a million Syrian civilians fleeing the fighting toward Turkey’s sealed border.
Turkey backs the Syrian rebels fighting in Idlib province, and has sent thousands of troops into the area.
Idlib is the last opposition-held stronghold in Syria.
A Turkish official said the fighting in Idlib was directly linked to Turkey’s decision to open the gates for refugees to Europe.
He said Ankara had changed its focus to preparing for the possibility of new arrivals from Syria "instead of preventing refugees who intend to migrate to Europe".
“Europe and others must take robust action to address this monumental challenge,” said Fahrettin Altun, the communications director for Turkey’s president, Recep Tayyip Erdogan.
“We can’t be expected to do this on our own.”
Mr Erdogan’s decision to declare his country’s borders with Europe open made good on a longstanding threat to let refugees into the continent.
His announcement marked a dramatic departure from the current policy and an apparent attempt to pressure Europe into offering Turkey more support in dealing with the fallout from the Syrian war to its south.
Under a €6 billion deal in 2016, Turkey agreed to stem the tide of refugees to Europe in return for financial aid, after more than a million people entered Europe in 2015.
It has since accused the EU of failing to honour the agreement, and Mr Erdogan has frequently threatened to allow refugees and migrants to head to Europe unless more international support was provided.
Turkey already hosts 3.6 million Syrian refugees, as well as others from Africa, Asia and the Middle East.
On the Greek-Turkish land border, Greek army and police patrols thwarted attempts overnight by thousands to push into the country, using tear gas and stun grenades to keep crowds back.
Officials said the situation was much calmer Sunday morning. But in the afternoon, authorities used tear gas and water cannons to push back another crowd attempting to cross.
Migrants threw rocks and other objects, and one policeman was injured.
The United Nations migration organisation reported at least 13,000 people had massed on Turkey's land border by Saturday night, most of them apparently from Afghanistan.
On the Greek islands, initial figures showed about 500 people had arrived from the nearby Turkish coast by Sunday afternoon.
If the trend continued, it would mark an increase in the usual number of people who arrive on eastern Aegean islands from Turkey.
Existing migrant camps on the islands are already dramatically overcrowded, and tensions there have mounted.
In a small harbour on Lesbos, angry local residents refused to allow migrants, including families with young children and babies, to disembark from a dinghy that had just arrived.
Groups of migrants who arrived on other parts of the island remained there for hours because local people prevented buses from reaching them to transport them to the main camp.
More than 19,300 people already live in and around the island’s migrant camp, which has a capacity of 2,840.
Protests by residents last week over the migrant situation degenerated into clashes with riot police on Lesbos and Chios.
Greece said it was using “all available means” to tell migrants that the country’s borders were closed, including text messages to foreign mobile phones in the border area.
In Syria, fighting escalated on the ground and in the skies.
Syria’s official news agency Sana said the four pilots ejected and landed safely after their two jets were shot down.
Turkey’s defence ministry said it had hit the two SU-24 aircraft as well as Syrian air defence systems after one of its aerial drones was downed.
Earlier on Sunday, Syria said northwestern airspace was closed and any aircraft or drone that entered “will be treated as hostile and shot down”.
The Syrian announcement followed two days of Turkish drone strikes in Idlib province.
Syrian activists said the strikes killed more than 50 Syrian government forces and allied fighters.
Turkey has lost 54 soldiers in February, including 33 killed Thursday in a single airstrike.
Outraged, Mr Erdogan announced his country’s European borders were open on Saturday.
The crisis in Idlib stems from a Syrian government offensive with Russian military support, which began on December 1st. – PA