Three bombs have exploded outside a police station in the Greek capital, Athens, just 100 days before the start of the Olympic Games.
Cars were wrecked and windows in nearby buildings shattered
They injured a policeman and badly damaged the station in the central district of Kalithea, near several hotels to be used by Olympic officials.
A newspaper in the city had received an anonymous telephone warning about 10 minutes before the pre-dawn blasts.
No-one has admitted responsibility for the attack.
Police believe the bombs - each reportedly made from three sticks of dynamite
triggered by alarm clocks - were linked to left-wing domestic groups
and not international terrorism.
They said they believed the timing of the explosions was staggered in the hope that the second and third bombs would injure police officers arriving at the scene after the first blast.
The BBC's Richard Galpin in Athens says left-wing groups oppose August's Olympic Games, viewing them as a capitalist bonanza, and have protested at Western security services arriving en masse in Greece.
The Greek authorities have sought to play down the significance of the blasts.
"This is an isolated incident which does not affect whatsoever
the country's preparations for the safety of the Olympics," Prime Minister Costas Karamanlis told reporters.
"The Greek people's efforts and their close co-operation with the
relevant authorities in the European Union, Nato and the United
States guarantee the safety of the Athens Olympic Games."
The Athens Games will be the first summer Olympics since the
September 11 2001 attacks in the United States.
Athens has allocated tens of thousands of police officers and army personnel
to ensure security at the games.
A city-wide network of surveillance cameras will be in operation, and aerial
patrols will take place.
A Greek delegation, led by Public Order Minister George Voulgarakis and
the head of the Greek police, is currently in Washington
for talks on the effort to safeguard the games.
Some US officials have expressed worry that construction
delays at Olympic venues could undercut efforts for advance
security testing and other measures.
Australian Foreign Minister Alexander Downer said
Australia's intelligence agencies would reassess the threat of a
terrorist attack at the Olympics.
"On the face of it, it doesn't look as though these
incidents are too serious but with the Olympic Games coming
up we want to be absolutely sure," he said.
A spokeswoman for the International Olympic Committee, Giselle Davies, said no formal approach had been made to the organisation by any national Olympic committee.
"Obviously it's an incident which is not connected with an
Olympic venue," she said, adding: "We understand it's a relatively small incident."
But a former British Heritage Minister, David Mellor, told the BBC: "Everyone is on notice now that if determined people want to do something
awful in Athens, the place has no serious controls to stop them."
History of attacks
The Greek authorities claimed they had crippled the most dangerous
domestic terrorist threat following the convictions last
year of 19 members of the November 17 group, blamed for 23 killings
and dozens of other attacks since 1975.
But smaller groups have continued to carry out bombings
and arson attacks in Athens and other cities.
In September, bombs damaged a judicial
complex in Athens and injured one police officer. The bombings were claimed by a group
calling itself Revolutionary Struggle.
Last month, the US state department's annual report on
terrorism said the "low-level bombings against an array of
perceived establishment and so-called imperialist targets... underscore the lingering nature of left-wing terrorism