Greek Citizen Protection Minister Michalis Chrisohoidis confirmed late Thursday that his personal security chief was killed when a bomb disguised as a gift exploded inside his ministry.

Police guard the entrance to the Greek Citizen Protection Ministry in Athens after a parcel bomb attack on June 24, 2010. Greek Citizen Protection Minister Michalis Chrisohoidis confirmed on Thursday evening that one police officer died during an unprecedented terrorist attack inside the building of the ministry. [Marios Lolos/Xinhua]

Police officer Giorgos Vassilakis, a 50-year-old father of two and Chrisohoidis's longtime associate, received the bomb placed in a package sent to him as a gift.

Chrisohoidis said the package had been intended for him. Most local media said he was in his office at the moment of the explosion.

"The Greek society will not be terrorized," said Chrisohoidis in the first comments to the Greek media after the terror attack, the first of its kind in Greek history.

Terrorists had never before penetrated into the office of a government minister in charge of public order.

The victim's office is next to Chrisohoidis's office on the seventh floor of the building.

Greek state television NET reported that another one was slightly injured by the blast that had collapsed walls and shattered windows.

Police stand guard at the entrance of the Greek Citizen Protection Ministry building on June 24, 2010. [Xinhua]

The SKAI television channel reported that Greek Prime Minister George Papandreou was immediately informed of the terror attack.

Counter-terrorism experts spoke anonymously to Greek media that there was no warning before the explosion and they suspected local guerrilla groups that had launched a series of attacks over the past decade against political, police and financial targets in the country were responsible for the attack.

Some counter-terrorism experts said that "Conspiracy of the Nuclei of Fire" could be behind Thursday's attack. The group has acclaimed responsibility for two earlier attacks outside the main prison of Athens and the courthouse of the northern city of Thessaloniki this spring. Two people were injured in the attacks.

Other security experts suspected that the attack could be organized by members of the "Revolutionary Struggle" group which has claimed responsibility for a major attack against the U.S. embassy in Athens four years ago.

Greek authorities have arrested some people accused of being key members of the "Revolutionary Struggle" group.