Nine Turkish nationals suspected of belonging to leftwing extremist organisations were arrested Tuesday during an anti-terrorist operation in Athens, police said.
The arrests come just ten days before Turkish President Recep Tayyip Erdogan is to visit Greece.
The eight men and one woman were arrested following raids on three apartments near the centre of the Greek capital, according to a police source.
For many decades members of Kurdish organisations have fled to Greece, which has delicate relations with neighbouring Turkey because of historic land claims.
Turkey is also unhappy that Greece has given sanctuary to suspects wanted over the 2016 failed coup, notably eight officers who escaped by helicopter on the putsch night.
However, the two countries are cooperating over the migrant crisis, following a deal between Turkey and the EU which has significantly stemmed the flow of people from Turkey to Europe.
Erdogan is to visit Turkey's NATO ally on December 7-8 -- the first to Greece by a Turkish head of state in 65 years.