Turkish President Recep Tayyip Erdogan has said that his country may reopen the route for refugees and migrants into Europe if it does not receive adequate international support to enable it to cope with the millions of refugees in Turkey.
"This either happens or otherwise we will have to open the gates," Erdogan said in a speech in the capital, Ankara, on Tuesday.
"Either you will provide support, or excuse us, but we are not going to carry this weight alone. We have not been able to get help from the international community, namely the European Union."
The Turkish government says it has only received a fraction of the promised financial support from the bloc.
The number of refugee arrivals in neighbouring Greece spiked last month. A week ago, more than a dozen boats carrying 600 migrants and refugees had arrived - the first simultaneous arrival of its kind in three years.
'We are ready'
Turkey, which hosts about 3.6 million Syrian refugees, controls parts of northern Syria where it says 350,000 Syrians have already returned.
"We are saying we should form such a safe zone that we, as Turkey, can build towns here in lieu of the tent cities. Let's carry them to the safe zones there," Erdogan said.
"Give us logistical support and we can go build housing at 30km depth in northern Syria. This way, we can provide them with humanitarian living conditions, he added."
"Our goal is for at least one million of our Syrian brothers to return to the safe zone we will form along our 450km border," Erdogan said.
The US-Turkey deal for the safe zone agreed last month is intended to manage tensions between Turkey and US-backed Kurdish-led forces over the border in war-torn Syria that Ankara brands as "terrorists".
The details of the plan are still unclear as is the size of the "safe zone" and how it will be managed or divided.