Greek security officials declared there are no terrorist groups or cells within the country's borders that pose a threat to the Olympic Games in August, despite a claim made by a militant group Thursday that it had dynamited a police station here last week to protest the coming influx of tourists, business executives and world leaders.

In a statement published Thursday in the weekly newspaper To Pontiki, a group called Revolutionary Struggle took responsibility for the May 5 triple bombing and said it carried out the attack to show the "vulnerability" of Greece's security measures. Although it did not threaten future strikes, the group denounced "wealthy" Western visitors and business leaders who are planning to attend the Olympics as "undesirable."

Another, smaller bombing damaged a Greek bank here Thursday, and authorities said they also found two explosive devices at a British bank nearby. No one claimed responsibility for those incidents, which did not result in injuries.

Greek authorities had played down last week's bombings, which occurred in the pre-dawn hours and injured no one, as the work of anarchists who regularly set off minor explosions with the intent of making political statements but not harming people. Government officials had also stated repeatedly that last week's attack was in no way tied to the Olympics, even though it occurred precisely 100 days before the Opening Ceremonies are scheduled to take place in Athens.

In an interview Wednesday, George Voulgarakis, the Greek minister for public order and the country's top security official, called the bombing "an isolated incident, in no way connected to the Olympics." Asked how he could be sure, given that authorities have not arrested anyone or named any suspects, he responded: "I have my sources."

In March the Revolutionary Struggle planted a crude bomb outside a Citibank branch that was defused by police. Authorities also believe the same outfit ignited two bombs at a local courthouse last September, wounding an officer.

Greek authorities, other Western officials and security experts said in interviews this week that they remained far less worried about such acts of violence than the possibility that Islamic radicals sympathetic to the al Qaeda terrorist network would try to slip into the country and stage a catastrophic attack on the Olympics.

"That specific incident was blown out of proportion," Spyros Capralos, Greece's general secretary for the Olympics, said of last week's explosion. "We've always had similar blasts that go off like that left and right."

The Greek government has said it will spend at least $1.2 billion to protect athletes and visitors to the Olympics and will deploy 70,000 police officers, troops and firefighters to provide security. Greece has also asked NATO to patrol the skies and waterways, and is relying on seven nations, including the United States, to provide intelligence on potential terrorist threats as well as other assistance.

Government and Olympic officials in recent days have gone to great lengths to convey a sense of safety, with some making blanket promises that no violence will break out during the Games, scheduled for Aug. 13-29.

"We guarantee a safe Games," Fanny Palli-Petralia, the deputy minister of culture, whose agency is overseeing preparations for the Olympics, said in an interview. "From July on, the most safe place in the world will be Athens and Greece."

Darryl Seibel, spokesman for the U.S. Olympic Committee, said Thursday the organization remains confident in Greece's preparations.

"We know this is a matter being addressed by the authorities in Greece," USOC spokesman Darryl Seibel said. "It hasn't caused us any additional or undue concern."

On Friday, the Greek government and its allies will begin a three-day security exercise to practice their response to potential terrorist strikes. On May 20, Greek Prime Minister Costas Karamanlis is scheduled to visit Washington to meet with President Bush to discuss the Olympics, with security the main subject. Greece has worked closely with the United States to coordinate intelligence efforts and training for the Games. Last week, Voulgarakis was in Washington to brief Homeland Security Secretary Tom Ridge, the CIA and State Department officials.

In the interview, Voulgarakis said the subject of last week's police precinct bombing didn't even come up during his visit, explaining that neither U.S. nor Greek officials saw the perpetrators as a serious concern.

The security minister said flatly that there were no terrorist groups within Greece that had the capacity or the will to mount a serious attack during the Olympics. "We cannot see a threat. We do not have it in our picture," he said, fingering a strand of red worry beads as he sat in his office. "This is a small country, everybody knows everybody."

He also discounted the possibility that sleeper cells of Islamic militants or other radicals had already infiltrated the country in a manner similar to how the Sept. 11, 2001, plots were launched from inside the United States. "I know in talking about Greece that we do not, and have not, had such cells," he said. "Believe me, I know my country."

Greece has a long history of anti-Western sentiment and political violence, but the threats have rarely been religious in nature and Islamic radicals do not have a significant presence, said Mary Bossis, a counterterrorism adviser to the Greek government.

As for anarchists or shadowy groups such as Revolutionary Struggle, Bossis said she doubted they posed much of a threat for the Olympics, either. The most violent terrorist organization in Greece has been November 17, which was broken up by authorities more than a year ago after assassinating two dozen people since 1975, including four U.S. officials.

"We do still have a number of small groups that are very angry, they are against everything," she said. "We cannot deny the fact that they exist. They can be very annoying and they will continue to make some noise. But they are little. They are not dangerous."

A diplomatic source involved in security preparations for the Olympics said planners' main fear was that foreign Islamic militants sympathetic to al Qaeda will try to commit terrorism on a grand scale. "Our focus is the big spectacular," said the source, speaking on condition of anonymity. "The bombing last week was an event but not the story. The story is what are you doing to stop an al Qaeda or a variant of what happened in Madrid."

Security and terrorism experts said that geography makes Greece a vulnerable place. It is a bridge between Europe and the Middle East that is particularly difficult to patrol because of its winding coastline and thousands of islands. And as a member of the European Union, visitors arriving in Greece from fellow EU nations are not subject to immigration checks.

"You look at the difficulties our country has in protecting its borders, well, Greece is probably 20 years behind us," said Philip Giraldi, a former CIA base chief in Barcelona who oversaw security preparations for the 1992 Olympics there. "Bear in mind there are lots of Islamic radicals living in Europe with French and British and other passports, and they'll be able to travel to Greece without having their documents checked. . . . Terrorists will be able to get in the perimeter."

The centerpiece of the Greek security effort is a $320 million command-and-control center intended to link a network of 1,400 cameras, sensors and computers. But the setup is still under construction and is not expected to be ready for testing until next month at the earliest.

As part of an effort to counter any perceptions that Greece is not up to the challenge of protecting the Olympics, the government keeps escalating official figures detailing the scope of its security plan. For instance, in March the government said it would spend $800 million and put 38,000 police and other forces on patrol. This week, the budget had climbed to more than $1.2 billion and the size of the security contingent had almost doubled.

"We are doing our best in terms of security and we want the world to know," said Athens Deputy Mayor Theodore Skylakakis. "The problem is, nowhere in the world does there exist the notion of total security. That's something that's humanly impossible."

Staff writer Amy Shipley contributed to this report.

Police check for evidence after a triple bomb blast May 5 in an Athens suburb that a Greek terrorist group called Revolutionary Struggle took credit for.