Greek police fired teargas toward migrants who were gathered on its border with Turkey and demanding entry on Saturday, as a crisis over Syria abruptly moved onto the European Union's doorstep.
The Greek government reiterated its promise to keep migrants out.
"The government will do whatever it takes to protect its borders," government spokesman Stelios Petsas told reporters, adding that in the past 24 hours Greek authorities had averted attempts by 4,000 people to cross.