ISTANBUL -- The ambassador of Greece to Turkey was summoned by the Foreign Ministry to discuss concerns regarding the activities of the Kurdish Workers Party, which is illegal in Turkey, according to state-run Anadolu news agency.

Turkish officials complained about Ambassador Christodoulos Lazaris's conduct in Greece by the Kurdistan Workers Party (or PKK), Anadolu reported Friday night, citing diplomatic sources.

They also expressed concern about the recent protest near Athens Turkish Embassy by PKK supporters, and the safety of Turkish citizens in Greece.

Tens of thousands have been killed during the 38-year-old insurgency waged by the PKK against Turkey. The U.S. and the European Union have designated it a terrorist organisation.

Turkey's main objection to NATO membership is the activities of terrorist groups in Sweden and Finland. After Russia's invasion in Ukraine, Ankara's concerns could impede their efforts to join NATO.

Turkey and Greece are at odds over many issues, including maritime borders in the Mediterranean Sea and Aegean Seas.

Recep Tayyip Erdan, Turkish President, stated Wednesday that Ankara had withdrawn from high-level negotiations with Athens. After a five year break, the mechanism to resolve disputes between traditional rivals was reopened last year.