Athens: A bomb blast early Monday caused minor damage to a building in Athens housing the headquarters of Greece's private radio and television network Skai, but there were no casualties, police said.
The homemade device went off at around 2.30am (0030 GMT), 45 minutes after an anonymous telephone warning to another TV network.
Police cordoned off the neighbourhood and evacuated the building that contains Skai, a group owned by the Alafouzos shipping family.
Police said the bomb was placed near the fence around the building and smashed windows in the main entrance.
The minister for civil protection, Olga Gerovassili, visited the site with police.
"The democracy is not threatened," she said, and warned those who "leave the way open to terrorism or fascism."
Anti-terrorist police opened an investigation that focused on Greek extremist groups.
Attacks targeting broadcasting groups, public companies or embassies have been frequent in Greece in recent years, and have been blamed on anarchist or far-left groups.
Last month a bomb was defused outside the Athens home of a controversial prosecutor.