The EU-Turkey pact that has since 2016 limited migration to Europe is "dead", the Greek Prime Minster has said.
Kyriakos Mitsotakis accused Turkey of "assisting" an ongoing surge of thousands of migrants on the border.
"Right now, let's be honest, the agreement is dead," he told CNN.
"And it's dead because Turkey has decided to completely violate the agreement, because of what happened in Syria," he added.
Thousands of migrants have gathered at the border since Turkish President Recep Tayyip Erdogan said last week that his country would no longer stop them from trying to leave.
The announcement came after dozens of Turkish troops were killed in an air strike in Syria.
Since then, Greek forces say they have prevented nearly 39,000 people from crossing the border. Turkey claims the real number is more than three times higher.
Turkey agreed in 2016 to stop letting migrants leave in exchange for €6bn, but Turkey says other parts of the EU deal including improved visa and trade rules were never fulfilled.
Mr Mitsotakis said Turkey was doing "the exact opposite" of its obligation to hold back asylum-seekers.
"They have systematically assisted, both at land and at sea, people in their effort to cross into Greece," he said.
He acknowledged that Turkey was hosting nearly four million refugees from Syria but insisted that "Europe is not going to be blackmailed over this problem by Turkey."
"We are not the ones escalating this conflict... we have every right... to protect our sovereign borders," he said.
Tension flared at Greece's mainland border with Turkey today as volleys of tear gas were fired from the Turkish side of the fence towards Greek border guards.
There has been a standoff in the border area of Kastanies since 28 February, when Ankara said it would no longer abide by the deal with the EU.
A Reuters correspondent saw Greek forces use a water cannon in an attempt to disperse people crowding at the border. It was followed by a volley of tear gas from the other side.
"(The) attacks are coordinated by drones. Apart from intimidation, these attacks are taking place from the Turkish police to help migrants cross the fence border line," a Greek government official said.
Turkey has said any tear gas fired is in response to teargas fired from the Greek side. "Why would Turkey fire tear gas to the Greek side of the border?" Interior Minister Suleyman Soylu told reporters after visiting the border area yesterday.
"Greece is firing tear gas at us, they are firing tear gas at our police stations at the border. We are responding to that."
Both sides used tear gas at the Kastanies border post on Wednesday.
Turkey has accused Greek forces of shooting dead four migrants, a charge rejected by Athens, which says Turkish forces are helping the migrants to cross the border.
Athens has called the confrontations a threat to national security and Prime Minister Kyriakos Mitsotakis brought European Union leaders to the area to press his case for support to avoid a repeat of 2015, when tens of thousands of asylum seekers poured into the European Union