Greek police have rounded up nearly 5,000 people in an operation targeting illegal immigration in Athens.
More than 1,130 people have been arrested in the capital since Saturday. More arrests are expected.
The crackdown comes amid fears the fighting in Syria could lead to a new influx of refugees.
More than 80% of migrants entering the European Union do so through Greece, which is in the grip of its worst recession in decades.
Some Greek politicians have called for the government to adopt a harder line on illegal immigration.
The BBC’s Mark Lowen in Athens says police have targeted migrants across the Greater Athens area.