Police said Saturday they had rounded up about 2,000 people in an operation to evict undocumented immigrants from central Athens, claiming that "national survival" was at stake for debt-choked Greece.
The aim of the operation was "to send them back to their countries of origin, close the borders and ensure that Athens returns to being a lawful city with a quality of life," police spokesman Christos Manouras said.
Operation Xenios Zeus, named after the name of the king of the ancient Greek gods in his role as protector of guests, mobilised 2,000 police in Athens and another 2,500 on Greece's eastern border with Turkey.
Manouras said the deportation of illegal immigrants was a necessity for national survival.
"We must send the message that Greece cannot afford work and hospitality" to would-be immigrants, he said.
Located in the southeastern extremity of the European Union, Greece has become a popular transit point for migrants from Asia or Africa seeking to enter the bloc.
But as the country struggles with a crippling economic crisis and sweeping austerity cuts, social tensions are on the rise and the increase in undocumented immigrants has fuelled xenophobia and racist attacks.
For the first time in Greek political history, the country in June voted into parliament a neo-Nazi party, Golden Dawn, which has promised to purge the country of illegal migrants.
Current figures show Greece has about 800,000 legally-registered immigrants, while the number of those without papers is estimated at more than 350,000.
On Wednesday police said they were tripling the number of guards along Greece's border with Turkey to 1,800 to ward off any influx of Syrian refugees.
The Athens operation launched on Thursday came as creditors from the International Monetary Fund, the European Union and the European Central Bank meet with Greek officials to discuss the further budget cuts needed to unlock the next tranche of aid in September, worth 31.5 billion euros.
Four months ago, Athens ran a similar eviction operation in conjunction with a number of city halls.
Right-wing Prime Minister Antonis Samaras, who took power in June at the head of a broad coalition, pledged during his election campaign to "win back the cities" and stop the "invasion" of immigrants.