The four men are believed to belong to the Revolutionary People's Liberation Party-Front (DHKP-C), a far-left armed group that has carried out attacks in Turkey, the source said.

Police found a Kalashnikov assault rifle, two submachine guns, three handguns, two grenades and over six kilogrammes (13 pounds) of gelatin dynamite at the apartment, the source said.

Last March, the DHKP-C claimed rocket and grenade attacks on the justice ministry and the ruling Justice and Development Party (AKP).

The group also claimed a suicide bomb attack on the US embassy in Ankara that killed a Turkish security agent on February 1.

The source said the latest case was apparently linked to the arrest of four men -- two Greeks and two Turks of Kurdish origin -- in July for transferring weapons and explosives to Turkey.

Greece's coastguard arrested the men off the Aegean island of Chios.