The Greek government has condemned the bombing of a major media group in Athens as an “attack by cowardly and dark forces against democracy itself.”

No injuries were reported in the powerful dead-of-night blast outside the offices of the Skai TV channel and radio network. The building also houses leading daily newspaper Kathimerini, which is part of the same media group. According to a police spokesman, anonymous warnings were phoned into a news website and a rival broadcaster about 45 minutes before the bomb went off at 2:37 a.m. Monday.

There was no immediate claim of responsibility.

Greece has a long history of political violence, and has witnessed a resurgence in domestic terror attacks in recent years that have targeted political parties, banks, government institutions and the media. At least two similar attacks in the past three years have been attributed to the far-left Popular Fighters’ Group, but the police declined to say whether Monday’s attack was by the same organization.

The police said a makeshift device, containing up to 10 kilograms (22 pounds) of explosives, had been placed inside a backpack and hung from a railing outside the building in Athens’ southern suburbs. The explosion caused extensive damage to the exterior of the building, with broken glass littering the pavement, and set off car alarms along the street.

Video footage broadcast on local media showed clouds of smoke billowing from the building. Scenes inside the Skai offices showed shattered windows and desks littered with debris.

Prime Minister Alexis Tsipras said in a short statement that the attackers “would not achieve their goal…neither to terrorize nor disorient.”

A statement by Skai, a free-to-air broadcaster that has been a fierce critic of Tsipras and his left-leaning Syriza party, criticized the government for ignoring repeated threats against it, while vowing to continue its duty of “checking power with independence and vigor.”

“The terrorist attack we received at dawn today will not hurt us. We are not intimidated, we are not afraid, we are not terrorized, as we have proven for many years.”