Police detained the alleged leader and another man in Paris on Saturday, while two others were detained Sunday in the northwestern communes of Evron and Saint-Ouen-l'Aumone.
The arrests were part of an investigation into terrorism financing and association with a terrorist group that was launched in July, the judicial sources said.
A source close to the case said investigators were probing whether the detained PKK members had been trying to obtain weapons of war.
The PKK, listed as a terrorist organisation by Turkey and by much of the international community, took up arms in Kurdish-majority southeastern Turkey in 1984, sparking a conflict that has claimed some 45,000 lives.
Turkish Prime Minister Recep Tayyip Erdogan accused France and Germany late last month of obstructing Ankara's fight against the PKK.
"On the contrary, they are letting the terrorist chiefs freely circulate in their countries," he told the private NTV television network.