Hijackers apparently linked to a militant Kurdish organization have hijacked a passenger ferry boat just southwest of the Turkish city of Istanbul.

Turkish Transport Minister Binali Yildirim said Friday as many as five hijackers had taken control of the boat and was holding passengers hostage.

Since the ferry was taken over earlier Friday there have been conflicting reports on the exact number of assailants and passengers.

At least one of the hijackers claims to have a bomb.

Turkish media reported that the ferry Kartepe was traveling on the Sea of Marmara toward Izmit, when the hijacker seized control of the vessel.

The Kurdistan Workers Party, or PKK, in recent months has increased its attacks against Turkish security forces with suicide bombings. The group claims to be fighting for increased civil and political rights in Turkey.

The United States and Turkey have labeled the PKK a terrorist organization.

Turkey's government has cracked down on anyone suspected of belonging to or collaborating with the PKK, saying the group is a growing threat. The military has launched a series of attacks against PKK bases along the country's border with Iraq.

Turkish coast guard vessels were following the hijacked ferry.

Izmit's mayor, Ibrahim Karaosmanoglu, had told local NTV that only one assailant was involved.

Details about the incident are still coming in. News reports say that between 17 to 23 people were on board the vessel.

More than 40,000 have died since the PKK took up arms against the Turkish government in 1984.

Attempts earlier this year to resolve the conflict failed.