A bomb exploded outside an Athens court on Thursday, causing damage but no injuries nearly two weeks before the trial of anarchists linked to a parcel bomb campaign targeting embassies and foreign leaders.

The blast smashed windows in the administrative court complex and in neighbouring buildings, mangling several vehicles parked outside and hurling debris over a wide area, news reports said.

Police had evacuated the area following a phone tipoff that revealed the license plate of a stolen motorcycle carrying the bomb, a police source said.

Earlier Thursday, television footage showed flames and smoke billowing in front of the court in the district of Ambelokipi near the city centre shortly after the device detonated

"My house shook and I saw bright red flames leaping to a height of fivemetres," a local resident told Flash radio.

Early information indicated that the device was probably a time bomb containing industrial-grade explosives given the strength of the blast, the police said.

The device was likely a fertiliser bomb consisting of ammonium nitrate, an explosive commonly used by Greek far-left extremist groups.

"It was a rather strong explosion," a local kiosk owner told Alter television, which received a warning phone call some 40 minutes before the blast and notified the police.

"I am 100 metres away and all my wares have fallen off the shelves," he said.

Left-wing Eleftherotypia daily also received a phone call prior to the attack, the police source said.

The government condemned the incident, with spokesman George Petalotis telling Flash: "The perpetrators of such acts will get their answer from the Greek people."

And Justice Minister Haris Kastanidis, who visited the stricken building, told reporters: "Terrorist attacks do not intimidate democracy."

There was no claim of responsibility for the bombing.

But the incident comes just over a fortnight before the scheduled trial of more than a dozen suspected members of a radical Greek anarchist group, Conspiracy of Fire Nuclei.

The court targeted on Thursday is responsible for civil cases and will not be handling the January 17 trial of the suspected extremists.

Conspiracy of Fire Nuclei was held responsible for a wave of parcel bombings in November that targeted foreign embassies in Athens and European government leaders, including French President Nicolas Sarkozy, German Chancellor Angela Merkel and Italian Prime Minister Silvio Berlusconi.

At least four of the parcels, which contained gunpowder, ignited and one of them burned the hands of a woman working at a courier company.

Last week, a similar campaign in Rome using stronger explosives injured two people at the embassies of Switzerland and Chile.

The Rome plot was claimed by an Italian anarchist group calling itself the Informal Federation of Anarchy, or FAI under its Italian acronym, which has expressed solidarity with jailed Greek suspected militants.

Another parcel attributed to FAI turned up at the Greek embassy in Rome on Monday but was deactivated before causing injury.

In an apparent link to Greek extremism, a note was found by police after the Chilean embassy blast, claiming the attack on behalf of the "Lambros Fountas Cell" -- a reference to a Greek militant shot dead by police in March 2010.

Fountas was a suspected member of another Greek far-left group, Revolutionary Struggle, which had carried out over a dozen attacks including a rocket strike against the American embassy in Athens three years ago.

After his death, police tracked down and arrested six other alleged Revolutionary Struggle members. Their trial is also expected in 2011.