The PKK, listed as a terrorist group by Ankara and much of the international community, including the EU and the United States, is believed to get political and financial support from many European countries.

It is not enough to list the PKK as a terror organization, but it is necessary to sincerely to take action against it, Erdogan said in the letter.

He called on the leaders to take steps aimed at destroying the PKK's network in Europe as soon as possible.

Erdogan also reminded that the PKK leaders were allowed free movement throughout European countries, and that European leaders continue to ignore Turkish demands to extradite known terrorists to Turkey.