Athens - Earlier today, a Greek policeman was seriously injured by some unknown attackers who threw a grenade and also fired shots at a police watch post.

At Athens hospital, a spokesman said "the condition of the wounded (policeman) is extremely serious but stable." The bullets had injured his lungs and other organs and the policeman had had to receive blood transfusions.

Greek Interior Minister Prokopis Pavlopoulos quickly condemned the attack.

"This was an attack on our democracy and on normality. The perpetrators will be swiftly apprehended, to secure our democracy," he said on television.

Police said the attack took place shortly after 3 am outside a Culture Ministry building in the central Athens district of Exarchia, an area considered a bastion of the city's anarchists who have carried out much of the violence of the last month.

Eyewitnesses spoke of two or three attackers who opened fire at the police watch post from about 40 metres. The policeman was hit on his upper body and leg. It was later determined that a hand grenade had also been thrown.

Police closed off the area and took 72 suspects into custody, Greek state radio reported.

Experts have classed the attack as a possible act of revenge, following the deadly shooting of a 15-year-old by police on December 6. Since then, Greece has been beset by violent protests.

On December 23, unknown attackers opened fire on a police bus. No one was injured in that attack, for which an unknown group calling itself "Peoples Action" claimed responsibility.

Police found at least 27 bullet shells which helped indentify the weapons used. One was an AK-47 Kalashnikov, previously used during the attack on December 23, state radio reported.

Four bullet casings came from a 9mm pistol, which had also been used during an attack on a police station by the terror organisation "Revolutionary Struggle".

This group is considered to be extremely dangerous, and has carried out several bomb attacks on government buildings and police cars during the last ten years, including an attack on the American Embassy in Athens two years ago.

The police are expecting members of "Revolutionary Struggle" to claim responsibility for this latest attack in the coming days.