Transportation Minister Binali Yıldırım said there were four or five assailants on the “Kartepe” ferry, which was hijacked when it was travelling between İzmit and Gölcük in the Gulf of İzmit when it was hijacked around 5.45 pm (1545 GMT). The assailants said they were acting on behalf of a wing of the terrorist Kurdistan Workers' Party (PKK) but did not make any demand yet, Yıldırım told private broadcaster NTV.
Earlier reports said the assailants wanted access to media.
İbrahim Karaosmanoğlu, the mayor of Kocaeli, which is located on the Gulf of İzmit, said one assailant had told the crew he was from the PKK.
"The person hijacking the ferry said he was a member of the PKK and wanted to draw attention to it in the media," Karaosmanoğlu told broadcasters.
There were 19 passengers and 6 crew on the ferry, according to Yıldırım, who said the authorities were able to contact captain of the ship. The terrorist who is with the captain says he carries a bomb, the minister also said.
Coastguard vessels are trecking the ferry as it zig-zags its way across the Sea of Marmara, east of İstanbul, Yıldırım said.
Whether the ferry has a destination is not clear. “We do not know what the destination would be. Right now, it is drawing zig-zags,” Yıldırım said.
Abdullah Öcalan, the jailed leader of the PKK, is held in a prison in an island off İstanbul.
The pro-PKK Fırat news agency, without citing sources, said the ferry was allegedly heading toward the heavily guarded prison island of İmralı, where Öcalan is serving life in prison.
Other ferry services in the Sea of Marmara were suspended as a precaution.
Yıldırım, who canceled a visit to the eastern province of Erzurum after the hijacking, said the ferry currently has enough fuel to travel 100-120 miles at full speed.
He said he was only able to receive limited information from the ferry but he had not received any communication to suggest any of the passengers had been harmed.