Greek police say they face growing public hostility after the recent riots
A Greek riot policeman has been seriously injured by two men with Kalashnikov automatic weapons in central Athens, officials say.
The officer was part of a unit guarding the culture ministry when the pre-dawn attack took place.
The policeman was taken to hospital and was undergoing surgery.
A huge manhunt is under way. Last month Greece saw its worst riots in decades after the fatal shooting by police of a teenager in Athens.
Police say 20 shots were fired by the attackers.
They say the 21-year-old officer spotted the gunmen and warned his colleagues shortly before he was hit by two bullets, one in the chest, the other in the leg.
A number of people have been taken in for questioning.
The incident took place in the Exarchia district, close to where Athens teenager Alexandros Grigoropoulos was shot by a policeman last month.
His death sparked weeks of clashes between rioters and security forces.
The policeman accused of shooting the teenager has been charged with murder.
The police want to discover whether the Kalashnikovs were the same ones used in late December when two gunmen hidden within the grounds of Athens University opened fire at a riot police bus as it passed by.
None of about 20 police on board the bus at the time were injured.
The BBC's Malcolm Brabant in Athens says police have been subjected to almost daily attacks from rioters since Alexis Grigoropoulos was killed.
Our correspondent says there is a fear that the current vehement anti-establishment climate in Greece may lead to a resurgence in domestic terrorism.