ATHENS - A GREEK riot police unit came under attack by at least one gunman in downtown Athens early on Monday, leaving one policeman seriously wounded, authorities said.

The pre-dawn attack by at least one gunman was aimed at a riot police unit guarding the Culture Ministry in the centre of the capital, police spokesman Panagiotis Stathis said, adding that the policeman had been hospitalized in serious condition.

Mr Stathis said several people had been detained in the nearby area of Exarchia as police searched for the attacker. He said no information was initially available on the number of detentions.

Greece saw its worst riots in decades after the fatal police shooting of a teenager in the Exarchia district on Dec 6. The death of 15-year-old Alexandros Grigoropoulos sparked near nightly clashes between riot police and youths throwing rocks and gasoline bombs, while police themselves have come under attack, with police stations being firebombed during the riots.

The street violence has now largely abated. But Monday's attack came nearly two weeks after a similar shooting in Athens, in which gunmen fired two automatic rifles at a riot police bus as it passed by a university campus outside the city centre on Dec 23. None of the about 20 police on board the bus at the time were injured.

A previously unknown group had claimed responsibility for that shooting, and a public prosecutor who handles terrorism offenses was heading the investigation into that attack.

At least six serious attacks have been carried out by little-known domestic radical groups in the past five years, including two bombings and the murder of a policeman by gunmen who stole his automatic weapon.

Most of these attacks were claimed by a group called Revolutionary Struggle. -- AP