The Rapid Border Intervention Teams set up in 2007 "are activated today for the first time", the European Commission said late on Sunday.

The Commission said the flows of illegal migrants entering Greece had "reached alarming proportions". It recorded a six-fold increase there in the number of Afghans trying to enter Greece in the second quarter of this year.

In total during that period, 90 percent of the migrants detected trying to enter the EU illegally were on the Greek land border, Frontex says.

Half of those detected were Albanian workers looking for seasonal jobs in Greece, Frontex says. Albania borders on northwestern Greece. But the other half - 9,500 - were migrants intent on travelling through Greece to settle in other EU member states.

Greece reported a total of 45,000 illegal border crossings for the first half of this year.

The European Commissioner for Home Affairs, Cecilia Malmstroem, said illegal migration was particularly "dramatic" along a 12.5km (eight-mile) stretch near the Greek town of Orestiada.

The EU is already helping Greece with money and other resources to reform its asylum system.

The UN has recommended that EU member states stop returning migrants to Greece, arguing that the detention conditions there are inadequate and that migrants risk "refoulement" - transfer to places where their lives or freedoms could be at risk.