At least 18 people drowned off the Turkish coast while trying to reach Greece today, while Macedonian authorities imposed further restrictions on refugees trying to cross the Greek border.
The Turkish coast guard launched a search-and-rescue mission for other migrants believed to be missing from the accident, the state-run Anadolu Agency reported.
The coast guard rescued 15 other migrants off the Aegean Sea resort of Didim, it added.
The dead included three children, according to private Dogan news agency.
Meanwhile, Greek police officials said Macedonian authorities are only allowing those from cities they consider to be at war to cross the Idomeni border crossing from Greece.
That means people from cities such as Aleppo in Syria, for example, can enter, but those from the Syrian capital of Damascus or the Iraqi capital of Baghdad are being stopped.
The two officials spoke on condition of anonymity because they weren't authorized to speak on the record.
The developments come a day ahead of a summit between the European Union and Turkey to discuss the crisis.
Nearly all refugees and other migrants who enter the EU have been doing so by taking small inflatable dinghies from the Turkish coast to the nearby Greek islands. With thousands of kilometres of coastline, Greece says it cannot staunch the flow unless Turkey stops the boats from leaving its shores.
Athens has also criticized Europe for not sticking to agreements to take in refugees in a relocation scheme that never really got off the ground.
"While Idomeni is closed for refugees and the flows from the islands, from the Turkish shores to the islands, remain, it must be perfectly clear that the immediate start of a reliable process of relocation of refugees from our country to other countries of the European Union is a matter of complete urgency," Prime Minister Alexis Tsipras said Sunday during a speech to his party.
"And this is exactly what we will seek in the summit on Monday. Not just the wording that this is urgent, but that it will begin immediately and with a large number," Tsipras said.
While thousands arrive in Greece's main port of Piraeus from the islands, about 13,000-14,000 people remain stranded in Idomeni, with more arriving each day. The refugee camp has overflowed, with thousands pitching tents among the railway tracks and in adjacent fields.
The rate at which refugees are being allowed to cross had already been reduced to a trickle, with sometimes only a few dozen, or even nobody, being allowed to cross. Greek police said 240 people crossed between 6 am yesterday and the same time this morning.
