Turkish subscribers to state-owned Turk Telecom can no longer access YouTube from their computers, The Guardian newspaper reported.
The ban was ordered by the prosecutor's office in Istanbul over offensive videos posted by Greeks and Turks.
The newspaper said Greek videos reportedly accused Mustafa Kemal Ataturk, the founding president of the Turkish Republic, of homosexuality, while a Turkish user responded by calling Greece the birthplace of homosexuality.
It is illegal to criticize either Ataturk or Turkishness in Turkey, the newspaper said.
YouTube had reportedly agreed to take down the offending videos.