Three civilians have been slightly injured so far and 40 youngsters have been detained in Athens on Monday afternoon during clashes between protesters and police which gradually spread across the city center, according to the latest reports by Greek media, according to Xinhua.

A series of rallies to mark the second anniversary of the fatal police shooting of a teenager which sparked the worst riots in Greece in decades turned violent on Monday in a two-kilometres zone spreading from Syntagma square in front of the Greek parliament building to Exarchia.

Over the past four decades Exarchia is regarded as a bastion of far-left and anarchist groups who operate in Greece.

In this same area 16-year-old Alexandros Grigoropoulos was shot dead on December 6, 2008 by a policeman who recently was convicted to life imprisonment. Grigoropoulos` death was followed by a string of violent clashes across Greece for two weeks.

As students gathered on Monday evening to the spot where Grigoropoulos was killed to honor his memory with candles and flowers, Greek television channels broadcast that a group of 150 anarchists torched dustbins and cars around the Polythechnic School in Exarheia.

Earlier in the afternoon a woman was transferred to hospital in a state of shock amidst flares hurled by hooded youth and tear gas fired by anti-riot police near the old university of Athens. Furthermore, a man has been hit in the head by a rock and another passer-by was attacked by a group of protesters who suspected he was an undercover policeman.

According to local media reports, up to 40 persons have been detained already during clashes which first erupted on Monday noon in a series of demonstrations staged by students, Left parties, labor unions and anarchists.

The protests organized in Athens and other major cities across the country for the anniversary were marred by images of hooded youth smashing windows of banks and bus stops, throwing petrol bombs against police, and raising barricades with dust bins, despite the strict security measures Greek authorities have taken.

The city center is shut to traffic from Monday morning to Tuesday morning and at least 5,000 police officers have been deployed across the area.

In an interview aired on state television on Monday evening Grigoropoulos` mother Tzina Tsalikian announced the creation of a foundation named after the victim aiming to protect youth from mistreatment of authorities.

"I wish no other child will face what my son faced. He was shot in the head in cold blood. The Greek state should make anything possible to safeguard youths` rights," said Tsalikian.