Greece has placed a 40km (25-mile) fence and surveillance system on its border with Turkey amid concern over a new wave of migrants from Afghanistan.
"We cannot wait, passively, for the possible impact," Greece's Citizens' Protection Minister Michalis Chrisochoidis said on a visit to the region of Evros on Friday.
"Our borders will remain unbreakable."
His comments came as Turkey called on European countries to take responsibility for Afghan migrants.
In a telephone conversation with Greek Prime Minister Kyriakos Mitsotakis, Turkey's President Recep Tayyip Erdogan said a sharp increase in people leaving Afghanistan could pose "a serious challenge for everyone".
"A new wave of migration is inevitable if the necessary measures are not taken in Afghanistan and Iran," Mr Erdogan said.
The rapid takeover of Afghanistan by the Taliban, an Islamist militant group, has left some fearing for their lives and seeking to escape the country, often by any means necessary.
Mr Chrisochoidis said the crisis had created new "possibilities for migrant flows" into Europe.
Greece, which was on the frontline of the migrant crisis in 2015 when more than a million people escaping war and poverty in the Middle East crossed from Turkey into the EU, has said it may send back any Afghans that arrive illegally through the country.
Many of those who arrived in Greece during the migrant crisis left Greece and travelled north throughout Europe, but about 60,000 have remained in the country.
Last year, Athens temporarily blocked new asylum applications after Mr Erdogan said Turkey had "opened the doors" for migrants to travel to the EU.
The decision came as as result of an emergency meeting led by Turkish President R.Tayyip Erdogan following a deadly attack on Turkish forces in Idlib, Syria.
Turkey declared halting all preventive actions against immigrants willing to cross into EU countries, primarily Greece.
Immigrants will be able to access to EU through Turkey either by land or by sea Erdogan had said at the time.