Athens -- A Greek tax office was hit by a bomb blast Friday one day after a judge's car was blown up in a series of attacks in Athens blamed on far-left militants, police said.

An immigration organisation was targeted in a separate arson attack also blamed on leftist extremists, who have stepped up their strikes on government and business targets since the police killing of a teenager in December.

No one was injured in the latest attacks.

Police suspect that the far-left group Revolutionary Struggle was behind the attack on the building that houses the tax office and a McDonald's restaurant in the central district of Ambelokipi.

"Both the force of the blast and the methodology point to an extremist group, particularly Revolutionary Struggle," police spokesman Panagiotis Stathis told AFP.

The bomb had been placed under a disabled persons' ramp at the entrance of the building, a police statement said.

Half an hour before the early morning blast, which shattered windows and sparked a fire that was put out before it could spread, anonymous warnings were telephoned to two Greek dailies, police said.

Revolutionary Struggle, which features on the European Union's list of terrorist groups, more recently launched two strikes against US-based banking group Citibank and attacks on police that nearly killed a young officer.

Two years ago, it fired a rocket at the US embassy.

The tax office attack came a day after the service car of the chairman of the Council of State was gutted by a gas canister bomb that was planted under the vehicle, which was parked near Greece's top administrative court.

Judge Panagiotis Pikrammenos had just been appointed the previous day in a scheduled justice ministry handover.

"It's a symbolic strike, most likely the work of small (far-left) autonomous teams preaching civil disobedience," Stathis said.

"The building has no police outside, only security inside to maintain order during court proceedings," he added.

The offices and homes of senior judges, which are not always well guarded, are popular targets in attacks designed to embarrass the authorities.

In April 2007, extremists snatched a submachine gun from a policeman guarding the home of then Supreme Court president Romylos Kedikoglou and used the weapon to strafe a police station a few days later.

The same gun was later used to seriously wound a police officer in an attack claimed by Revolutionary Struggle, an outfit which emerged in 2003.

Extremists have intensified attacks on government and business targets since the police shooting in December, which sparked a wave of youth protests and violence that analysts say emboldened radical groups.

But despite a flurry of attacks since December police have been unable to make arrests. "There are a number of people under close surveillance but so far no evidence has surfaced to arrest them," a police source told AFP.

The attacks come despite repeated pledges by the government to increase security and to reactivate a network of surveillance cameras installed for the Athens 2004 Olympic Games.

In another attack early on Friday, the front entrance of the government-funded Hellenic Migration Policy Institute (IMEPO) was doused with petrol and set on fire, causing minor material damage but no injuries.

Police initially said the arsonists had used a gas cannister bomb.

No group claimed responsibility but police suspect far-left extremists were involved to send a message to the Interior Ministry, which uses IMEPO statistics for its tough immigration policy.

"The arsonists likely saw IMEPO as part of the state mechanism though we can't always attribute logic to these attacks," Stathis said.

AFP/Expatica