A policeman was shot and seriously injured in Athens early today as protesters sprayed automatic fire at officers guarding the Culture Ministry, prompting fears of renewed anarchist violence.

Diamantis Matzounis, the 21-year-old policeman, was reported to be in a critical but stable condition, with bullet wounds over his whole body from chest to legs. He had been one of three members of a ministry police guard fired on by two attackers using AK-47 assault rifles and at least one 9mm pistol.

The bohemian Exarchia district where the ministry is located was cordoned off and more than 70 people taken in for questioning. Thirty-four cartridges found at the scene were sent for ballistics tests.

"The attack appeared to be well-planned, with concentrated fire from at least two directions," said Nikos Karadimas, a police spokesman.

The use of AK-47s is worrying the police, as it has been one of the favourite weapons of the Albanian and Russian underworlds. A similar weapon was used in an attack on a police bus carrying a riot squad on December 23, with no casualties. Some believe that extremist groups might now be as well-armed as the notorious 17 November group that murdered 23 diplomats, police officers and and businessmen from 1975 to 2002, when it was uprooted with help from London's Metropolitan Police.

The shooting appeared to signal an early end to the unofficial holiday truce that Greece's anarchist groups had signalled they would keep, after nearly two weeks of destructive inner-city rioting last month.

Prokopis Pavlopoulos, the interior minister, said that the attackers would "soon realise that democracy is strong and society is protected". His government, though, is coming under growing public criticism for its perceived leniency towards rioters and the looters who operate in their wake.

The attack occurred less than half a dozen blocks from the Exarchia street where 15-year-old Alexander Grigoropoulos was fatally shot by a ricocheting police bullet on December 6, an incident that sparked Athens' worst civil disturbances in thirty years and anti-Greek demonstrations in European capitals.

Planned leftwing marches on the Israeli embassy in Athens today, to protest at the conflict in Gaza, were expected to widen into more general anti-police violence. There was renewed tension in the centre of Athens, as shoppers hurried through their pre-Epiphany Day purchases, fearing new outbreaks of rioting.

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