The proclamation by the group, calling itself Revolutionary Struggle, did not threaten to carry out future attacks. But its anger toward the unprecedented Olympic security measures could further shake international confidence about safety during the Aug. 13-29 Games.
"All members of international capital (multinational companies, business executives), global mercenary killers, the state officials and the wealthy Western tourists who plan on finding themselves at the games are undesirable," said the statement published in the weekly newspaper To Pontiki.
Greek government spokesman Theodoros Roussopoulos said authorities are "not worried." Police officials believe the declaration came from the same group that struck in September with twin bombings at a judicial complex that injured one officer.
The group said the May 5 blasts outside the police station in the suburb of Kalithea showed "vulnerability" and that the "famous dogma of total security is meaningless."
The attack, which caused limited damage but no injuries, occurred on the beginning of the 100-day countdown to the opening ceremony. Greek officials also were in Washington at the time for Olympic security talks.
The statement added that the Olympic security plan, which includes NATO assistance, has turned Athens into a "fortress" and "is not about a celebration, as organizers like to say, but about war."
Despite the proclamation's ominous tone, Greek urban guerrilla groups mostly wage pinpoint arson or bomb attacks on commercial, diplomatic or police targets. The blasts are usually timed late at night to avoid causalities.
Last week's bombings, however, appeared designed for bloodshed and rattled security forces leading an unprecedented Olympic protection network costing more than $1.2 billion.
The Greek government — which repeatedly insisted last week's bombings were not linked to the Olympics — tried to maintain a calm front. Roussopoulos said the proclamation would be treated with "seriousness and responsibility."
The bombings heightened worldwide anxiety about the security of the games — the first summer Olympics since the Sept. 11, 2001, attacks.
Australia issued a travel advisory on Greece and South Korea's gymnastics association said it was considering canceling plans to train in Athens.
Earlier Thursday, a firebomb damaged a branch of the private Alpha Bank. Two similar devices were found at a nearby branch of the London-based HSBC Bank but did not explode, authorities said. There was no immediate claim of responsibility.
Athens security chiefs, meanwhile, began a four-day simulated Olympic security exercise with senior American officials and advisers from six other countries, the public order ministry said.
The "Olympic Guardian II" exercise involves about 300 people and will examine "counter-terrorist response scenarios and management of the consequences" of an attack, a statement said.
Greece this month increased its Olympic security budget and boosted personnel to 70,000 police and soldiers in Athens and Olympic-related areas during the games.
Greek authorities claim they dismantled the most dangerous domestic terrorist threat following the convictions in December of 19 members of the group November 17, which is blamed for 23 killings and dozens of other attacks since 1975. Smaller groups have continued to wage low-level violence.