At a meeting of EU interior ministers in Brussels on Wednesday, the member states said that Turkey was exploiting refugees to get its way politically.
A joint statement said that bloc "strongly rejects" the "use" of migrants by Ankara, saying that the "situation at the EU's external borders is not acceptable."
"The EU and its member states remain determined to effectively protect EU’s external borders," the ministers wrote in the statement.
"Illegal crossings will not be tolerated. In this regard, the EU and its member states will take all necessary measures, in accordance with EU and international law ... Migrants should not be encouraged to endanger their lives by attempting illegal crossings by land or sea."
The interior ministers called on Turkey to "relay this message and counter the dissemination of false information."
Since Turkey's decision, the humanitarian situation has deteriorated both at the land border of Greece and Turkey and on the Greek island of Lesbos.
France accuses Turkey of 'blackmail'
European Council chief Charles Michel and the EU's top diplomat Josep Borrell were in Turkey on Wednesday as political rhetoric between Ankara and Brussels heated up.
Erdogan has said he will not renegotiate a refugee deal with Europe until the bloc agrees to support its military efforts in Syria, a move French Foreign Minister Jean-Yves Le Drian called "blackmail."
"This migratory pressure is organized," Le Drian said in Paris. "It is organized by President Erdogan's regime as a form of blackmail against the European Union."
In Ankara, Borrell said that during talks the EU had offered humanitarian aid worth 60 million euros for the most vulnerable groups of people in northwestern Syria, as well as additional assistance to Turkey in addressing its own specific "challenges stemming from the situation in Syria."
"Lives of people cannot be put at risk," he wrote on Twitter, stressing the importance of the EU and Turkey working together.
Why did Turkey open the border?
Borrell warned that Erdogan's decision to open its borders to Europe would deeply undermine trust, urging the Turkish president to return to his obligations from the 2016 agreement between Brussels and Ankara that saw Turkey vow to stop migrants from crossing to Greece in exchange for aid money and other concessions.
"Border and unilateral action don't benefit anyone" Borrell said in a speech in Ankara.
Earlier on Wednesday, Turkey accused Greek forces of having shot dead a refugee when they fired tear gas in an effort to repulse a group trying to cross the border. The Greek government responded by saying Turkey was spreading "fake news." It was the second such exchange of the week between the two governments.
On February 27, Erdogan announced that his government would no longer actively prevent the 3.6 million Syrian refugees it hosts from entering Europe, after 33 Turkish troops were killed during airstrikes in Idlib carried out by the Syrian regime. Turkish forces have been fighting the Russian-backed Syrian army, as well as Kurdish combatants in the area, off and on since 2016.
Since then, the Turkish government had repeatedly threatened to "open the gates" to Europe during several disputes with the bloc.
ed, es/aw (AFP, dpa, Reuters)