A gunman fired a spray of bullets at the headquarters of Greece's governing centre-right New Democracy party near central Athens early Monday, with one hitting an office occasionally used by the prime minister, officials said. No one was hurt.

A government spokesman said the shooting was part of an effort to "terrorize" Greek society, which is struggling through its worst financial crisis in two generations amid a drastic fall in living standards and a record rise in unemployment.

Police cordoned off the area where unknown gunman shot at least nine automatic rifle rounds at the building on the capital's busy Syngrou Avenue, south of the city centre.

Wave of political violence

No group claimed responsibility for the pre-dawn attack, which follows a renewed wave of low-scale politically motivated violence by small anarchist and far-left militants.

The belt-tightening, amid widespread disgust with an incompetent and often corrupt political establishment blamed for the country's woes, has boosted extremists both to the left and right of the political spectrum. A fringe ultra-right group accused of fostering violent attacks on dark-skinned immigrants is represented in Parliament and regularly polls as the country's third most popular party.

All political parties condemned Monday's attack.

"No act of terrorism is going to scare us," said Makis Voridis, a spokesman for New Democracy. "Our efforts to restore law and order ... will continue unobstructed."

His comments appeared to be a reference to recent police evacuations of anarchist squats in Athens, which triggered a series of firebomb attacks on journalists' homes, local branches of parties in Greece's governing coalition and cash machines.

Government spokesman Simos Kedikoglou said a "symbolic" bullet went through the window of the office used occasionally by Prime Minister Antonis Samaras and was found inside the room.

"There is a new worrying increase in efforts to terrorize our society," Kedikoglou said.

A policeman stands guard in front of the headquarters of co-ruling New Democracy party after an attack in Athens on Monday. (Yorgos Karahalis/Reuters)

No party officials were in the building at the time. The official prime minister's office is at another building in central Athens, where he spends most of his time.

"Of course there could have been (victims). There could have been a cleaner in the prime minister's office or a security guard at the site," Kedikoglou said.

Police said the attacker was believed to have had at least one accomplice, while experts were examining a car found abandoned and burned near the scene. The anti-terrorism squad is heading the investigation.

New Democracy heads a three-party coalition government formed after elections in June and is leading Greece's painful economic recovery effort to cut its high public debt and budget deficit through deeply resented spending cuts and tax hikes.

The austerity measures were demanded by international creditors in exchange for the vital bailout loans that have shielded Greece from bankruptcy since May 2010.

For decades, Greece was plagued by deadly far-left political violence that targeted police, government officials, businessmen and financial institutions. But the toughest groups were eradicated in a crackdown just before the 2004 Athens Olympics, and over the past three years authorities have arrested more than two dozen people over attacks by militant anarchists that caused extensive damage but no loss of life.

After authorities cleared two squats in Athens last week, the homes of five prominent journalists were firebombed. The attacks were claimed by small anarchist groups that accused their targets of serving the establishment.

Over the weekend, arsonists targeted the home of the brother of government spokesman Kedikoglou. The unknown attackers broke down the door with a sledgehammer and threw in a firebomb that exploded without causing injury.