A man looks out from a broken window after a bomb blast outside the Greek SKAI TV building in Athens.
ATHENS - A bomb blast early on Monday damaged a building in Athens housing the headquarters of Greece's private radio and television network Skai, but there were no casualties, police said.
Anti-terrorist police opened an investigation into the attack 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.
The coalition government led by leftist Prime Minister Alexis Tsipras condemned the blast as "an attack on democracy".
The homemade device went off at around 2.30am, 45 minutes after an anonymous telephone warning to another TV network.
Police cordoned off the neighbourhood in the Athens suburb of Neo Phaliro and evacuated the building, which contains the offices of Skai, a group owned by the Alafouzos shipping family, as well as those of Kathimerini, a centre-right daily critical of the government.
Police said the bomb was placed near a fence around the building and smashed windows on the facade.
Skai said in a statement the blast caused "major damage".
"The terrorist attack will not discourage us..," it said, accusing the government of failing to do enough to protect the media despite "recurrent threats against the station."
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."
Last month a bomb was defused outside the Athens home of a controversial prosecutor.