ATHENS, Greece - Three bombs exploded outside a police station today in a series of timed blasts, causing serious damage and rattling security forces just 100 days before the Olympic Games. No injuries were reported.

The pre-dawn explosions, which occurred within a half hour, came before events to mark the final stretch to the Aug. 13-29 Olympics. An anonymous caller to an Athens newspaper warned of the attacks about 10 minutes in advance, but gave no motive or claim of responsibility.

Police believe the bombings were linked to domestic groups and not international terrorism.

The bombs - each made from three sticks of dynamite triggered by alarm clocks - appeared timed to cause casualties despite the tip to the newspaper, police claimed. Parts of the building, which includes several police agencies, were damaged and windows were shattered in nearby apartment blocks in the densely populated Kalithea suburb.

"This is something very serious," Kalithea Mayor Constantinos Askounis told private Alpha radio. "It takes on a different dimension with the Olympics."

Authorities evacuated the station and cordoned off the area. The head of Greece's anti-terrorist squad was among the high-level personnel called to the site. Bomb experts also conducted a controlled explosion, but it was apparently a suspicious package and not a fourth bomb.

The Olympics carry a record security price tag of at least $1.2 billion that includes a planned citywide network of surveillance cameras and aerial patrols. The camera system is not yet in full operation.

A Greek delegation, led by the public order minister and the head of the Greek police, is currently in Washington for talks on efforts to safeguard the games - the first summer Olympics since the Sept. 11 attacks.

Some U.S. officials have expressed worry that construction delays at Olympic venues could undercut efforts for advance security testing and other measures.

"We were beginning to hear a lot of concerns about the preparations and whether we should go," said Sen. Gordon Smith, R-Ore., who added that he believed a U.S. presence at the games was important.

Australia's Olympic committee secretary general, Bob Elphinston, said the committee was not contemplating withdrawing the team from Athens but individual athletes were free to pull out.

"Any bomb that goes off in Athens is worrying," Elphinston said.

Australia - host of the 2000 Sydney Games - will also "review the existing threat assessment," said its foreign minister, Alexander Downer. Australia is part of a seven-nation security advisory panel for Athens that includes the United States.

In September, similar timed blasts damaged a judicial complex in Athens and injured one police officer. The twin bombings, spaced 20 minutes apart, were claimed by a group calling itself Revolutionary Struggle and believed to be a protest against crackdowns that toppled the deadly November 17 terrorist cell.

Greek authorities claimed they crippled the most dangerous domestic terrorist threat following the convictions in December of 19 members of the group, blamed for 23 killings and dozens of other attacks since 1975. The victims include four U.S. officials, two Turkish diplomats and a British defense envoy.

But smaller groups have continued to carry out bombings and arson attacks in Athens and other cities, but most are against cars and commercial targets and rarely cause injuries.

In April, the U.S. 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 in Greece."