The EU warned Turkey that failure to resolve the impasse between authorities and prisoners in which 20 hunger strikers have died could harm relations between Ankara and Brussels.
"We do not want Turkey's relations with the EU and with the European Parliament and the European public to be adversely affected in an unnecessary way," European MEPs Mr Daniel Cohn-Bendit and Mr Johannes Swoboda said after a two-day visit to Ankara.
"Every further death due to the hunger strikes would increase the concern and horror felt by the European Parliament and public," they said in a statement.
Human rights groups say some 800 inmates and relatives of prisoners are on hunger strike to protest against transfers from large dormitories to smaller cells that prisoners fear will make them more vulnerable to abuse by jailers.