ATHENS — Greece said it will stop accepting new asylum applications for a month and step up border security measures as an increasing number of migrants arrive through Turkey.

Prime Minister Kyriakos Mitsotakis said Sunday the national security council had decided to increase the “level of deterrence at our borders to the maximum.” He added that his government had invoked an article of the Treaty on the Functioning of the European Union that calls for the EU to adopt “provisional measures” to support a member country confronted by “an emergency situation characterised by a sudden inflow of nationals of third countries.”

Government spokesperson Stelios Petsas also said migrants will be returned immediately if possible without being registered.

Mitsotakis also said he would visit the country’s Evros land border with Turkey with European Council President Charles Michel on Tuesday and warned that anyone entering the country illegally would be turned away.

“The borders of Greece are the external borders of Europe. We will protect them,” Mitsotakis wrote on Twitter.

Michel voiced his “support for Greek efforts to protect the European borders” in his own tweet and said he is “closely monitoring the situation on the ground.”

Thousands of migrants have amassed at the border after Turkish officials said last week they would no longer work to stop migrants entering Europe, a stance reiterated by President Recep Tayyip Erdoğan on Saturday.

Greek authorities registered about 9,600 attempted border crossings overnight, Greek Deputy Defense Minister Alkiviadis Stefanis said Sunday, according to local media. Another 5,500 attempted border crossings were prevented by Sunday afternoon, government officials said. Around 500 migrants arrived on the islands of Lesbos, Chios and Samos by boat on Sunday.

The foreign affairs ministry accused Turkish authorities of giving false numbers on the number of migrants crossing, writing on Twitter that “10,000 people were prevented from entering Greek territory” between Saturday morning and Sunday morning.

The EU’s border protection agency Frontex also said Sunday it was deploying equipment and officers to Greece.

“Frontex is in close contact with Greek authorities regarding additional support we can provide. We are redeploying equipment and additional officers to Greece and closely monitoring the situation,” the agency wrote on Twitter.

A Frontex spokesperson said it is still unclear how many officers it would send to Greece because the agency is “still assessing the needs.” The spokesperson said Frontex is on “high alert” concerning the EU’s borders with Turkey and is monitoring the situation in Bulgaria, which also shares a land border with the country.

European Commission Vice President Margaritis Schinas tweeted Sunday he had requested an extraordinary meeting of EU interior ministers to “urgently” discuss the situation.

This article has been updated.