A bomb disguised as a gift exploded inside the Greek public order ministry in Athens yesterday night, killing a police officer who was a close ministerial aide, in Greece's highest profile attack in years.

"It was a terrorist act," government spokesman Giorgos Petalotis told the Associated Press.

Police said the package exploded about 25 metres away from public order minister Michalis Chryssohoidis's office on the seventh floor of the heavily guarded ministry, which is located just outside the capital's centre.

Mr Chryssohoidis, who was unharmed despite being in his office at the time of the blast, said he had "lost a valuable and beloved associate".

The police officer who was killed, Giorgos Vassilakis, was a 50-year-old father of two. Authorities said there were no other injuries, but that the powerful explosion had caused extensive damage inside the ministry.

"The cowardly murderers will be brought to justice, to be tried in accordance with the constitution and our laws," a visibly shaken Mr Chryssohoidis told media outside the ministry shortly after the explosion. "We will continue our struggle to keep our citizens, neighbourhoods and cities safe."

The minister said the package had been meant for him.

"We say one more time that we are not afraid and we will not be terrorised," he said.

There was no immediate claim of responsibility for the bombing.