Turkish warplanes repeatedly entered Greek airspace on Monday, the state ANA news agency said, as NATO prepared to deploy ships to the Aegean Sea against migrant smugglers.

The Athens News Agency said six warplanes and a navy transport plane had carried out over 20 violations of Greek national airspace near eastern and central Aegean islands.

Two of the planes were armed and mock dogfights occurred on two occasions when Greek fighters moved to intercept, the agency said. No live rounds were exchanged.

The incident occurred as a NATO naval group was to launch patrols in the waters between the two countries to deter people-smugglers facilitating the influx of hundreds of thousands of refugees and migrants into Europe.

Albeit NATO allies, Greece and Turkey have a fraught history going back centuries and remain at loggerheads over territorial and airspace rights in the Aegean.

Athens fears that Ankara could exploit the refugee crisis to strengthen its presence in the Aegean, where it claims the waters and airspace surrounding many Greek islands near its coastline.

Greece and Turkey nearly went to war over a cluster of uninhabited Aegean Sea islets in 1996.

Athens has said it is keen to work with Turkey on stamping out people-smuggling networks, but it wants Ankara to apply a bilateral agreement on migrant re-admission which is currently all but inactive.

Thousands of migrants are still crossing the Aegean daily from Turkey -- with many dying in the attempt -- after over a million made the perilous journey last year.