The four are suspected of being members of the Revolutionary People's Liberation Party-Front, or DHKP-C, a group believed responsible for a string of bombings and assassinations in Turkey, including a suicide bombing against the US Embassy in Ankara last year that killed a guard and the bomber.
Police have said at least one of the four Turkish nationals was being sought by Turkey under an international arrest warrant, and that his DNA matched traces on weapons intercepted by Greek authorities in the Aegean Sea last summer on a speedboat allegedly headed for Turkey.
Police said one of the four jailed today is also linked with the Thessaloniki explosion.
