The imprisoned leader of a Kurdish guerrilla movement that has been waging a bloody insurgency against the Turkish state for decades called on Thursday for his fighters to lay down their arms.

The Kurdistan Workers’ Party, or P.K.K., is classified as a terrorist organization by Turkey, the United States and other countries. The group’s leader, Abdullah Ocalan, made his appeal in a written statement that was read aloud during a news conference by members of Turkey’s main pro-Kurdish political party who had just visited him in prison.

Mr. Ocalan called for the P.K.K. to lay down its weapons, saying in the statement that the group has completed its life-span and should disband.

The rare message from Mr. Ocalan raised the possibility that a conflict that has killed more than 40,000 people over four decades could finally end. It could also echo across borders, given Mr. Ocalan’s profound influence over members of the group in Turkey and Iraq as well as affiliated Kurdish militias in Syria and Iran.

But there was little indication of what would happen next. There has been scant public discussion of who would monitor compliance with Mr. Ocalan’s call, what would happen to fighters who comply with it or what — if anything — the government has offered in exchange for the disarmament.

Mr. Ocalan’s appeal came after a series of talks that included Turkish officials; Mr. Ocalan himself; and members of Turkey’s main pro-Kurdish party, the People’s Equality and Democracy Party, or D.E.M.