Turkey's President Recep Tayyip Erdogan has said his country's borders with Europe are open.
Mr Erdogan's announcement delivered on his long-standing threat to let refugees into the continent as thousands of migrants gathered at Turkey's border with Greece.
The announcement marks a dramatic departure from current policy and an apparent attempt to pressure Europe. It comes amid a military escalation in Syria's Idlib province that has forced hundreds of thousands of Syrian civilians to flee fighting between advancing Syrian government forces backed by Russia and rebel fighters supported by Turkey.
The mass displacement in Idlib has raised the possibility that Turkey might come under growing international pressure to open its now sealed border with Syria and offer refuge to desperate Syrian civilians.
"We can't handle a new wave of migration," Mr Erdogan said, in an apparent reference to the growing humanitarian crisis in Idlib. Nearly 950,000 displaced civilians have been pushed towards the Syrian-Turkish border amid cold winter weather.
Mr Erdogan said Turkey would not stand in the way of refugees and migrants already in the country who hope to head to Europe.
"We will not close the gates to refugees," he said. "The European Union has to keep its promises. We are not obliged to look after and feed so many refugees."
Under a 6 billion euro 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. Mr Erdogan has frequently threatened to "open the gates" and allow refugees and migrants to head to Europe unless more international support was provided.
Since seizing territory from Kurdish forces in a different part of Syria in October, Mr Erdogan has also suggested resettling at least a million Syrian refugees from Turkey in that region. However, his efforts to secure funding for such a scheme have been rejected by European governments. Aid groups have said it is still too dangerous to return refugees to Syria.
Turkey currently hosts more than 3.5 million Syrian refugees, and many others fleeing war and poverty in Asia, Africa and the Middle East use it as a staging post and transit point to reach Europe, usually through neighbouring Greece.
Migrants played a cat-and-mouse game with Greek border patrols on Friday night and throughout Saturday, with Greek authorities firing tear gas to repulse the crowd's attempts to push through the border. Greek officials said many migrants threw rocks at police and tear gas was fired towards the Greek border from the Turkish side.
Some migrants cut holes in the fence, with a few managing to get through. The vast majority were from Afghanistan and most were men, although there were also some families with young children. They took shelter overnight in abandoned buildings or small chapels in the Greek countryside before starting to walk towards northern cities.