Turkey says it is deploying 1,000 police officers to its land border with Greece to halt the pushback of migrants into Turkey.
Thousands of migrants and refugees, desperate to get into the EU, remain in the border zone. Greek guards have fired tear gas to stop them entering.
The extra Turkish police are going to the Meric river (called Evros in Greek) on the border, Interior Minister Suleyman Soylu said.
The EU has condemned Turkey's policy.
The Greek government says that since early Saturday its forces have prevented the illegal entry of 34,778 people and arrested 244.
Syrians, Afghans, Pakistanis and West Africans are among the migrants at the border.
EU solidarity with Greece
In a statement, the EU Council - representing the 27 foreign ministers - said the council "expresses its solidarity with Greece" and "strongly rejects Turkey's use of migratory pressure for political purposes".
"This situation at EU's external borders is not acceptable." The council demanded that Turkey implement the 2016 EU-Turkey agreement, which obliged Turkey to block illegal migration into Greece.
Turkey announced nearly a week ago that it would no longer enforce the 2016 deal, accusing the EU of inaction over Syrian war refugees. Turkey is already hosting some 3.7 million Syrians, and nearly a million more are on its southern border after fleeing from war-torn Idlib.
Turkish President Recep Tayyip Erdogan is meeting Russia's President Vladimir Putin in Moscow, in a new effort to reduce the Syrian tensions. Turkish forces are clashing with Russian-backed Syrian government troops in Idlib.
Meanwhile, Greece is struggling to cope with more than 20,000 asylum seekers on the island of Lesbos who are living in squalid, overcrowded camps. There has been local hostility towards new arrivals trying to come ashore from nearby Turkey.
Mr Soylu accused Greek forces of having wounded 164 people at the land border.
Turkish officials said a man was fatally wounded when Greek security forces opened fire on migrants on Wednesday. Greece denied that, as well as claims that two Syrians were fatally shot earlier on the border.
The River Evros is now heavily fortified, with Greek security personnel positioned on every few metres, a BBC correspondent reports.
How it started
When at least 50 Turkish soldiers were killed in northern Syria in late February, President Erdogan said Turkey was facing a major influx of people fleeing Russian and Syrian air strikes.
Although the EU promised billions more euros in aid, Turkey was unimpressed and decided to open its borders with Greece and even bussed migrants close to the north-western border.
Greece said this week that the migrants were being "manipulated as pawns" by Turkey in an attempt to exert diplomatic pressure. Greece has halted for a month all asylum claims from migrants who enter Greece illegally.
President Erdogan argued that the decision to open the border gates was "fully" in line with international law.
Top EU officials have visited the area, which serves as the bloc's south-eastern border, promising financial help to Greece to step up security.
European Commission President Ursula von der Leyen described Greece as a "European shield", using the Greek world aspida.
The EU's Frontex border agency plans to deploy extra guards and equipment to help Greek police.