Three home-made bombs exploded outside an Athens police station early Wednesday causing no injuries, but renewing fears about security in the Greek capital just 100 days before it hosts the 2004 Olympic Games.
The government blamed "local extremist elements," apparently a leftwing extremist group, for being behind the blasts, and Greek Prime Minister Costas Karamanlis vowed they would not jeopardise the security of the Games which start on August 13.
"This is an isolated incident which does not affect whatsoever the country's preparations for the safety of the Olympics," Karamanlis told reporters.
"The effort of the Greek people and their close co-operation with the relevant authorities of the European Union, Nato and the United States guarantee the safety of the Athens Olympic Games," Karamanlis added.
The Games, the first Summer Olympics to be held since the September 11, 2001 attacks, will open amid unprecedented security, with Nato finalising a plan to provide air and sea surveillance and seven countries, including France, Britain, the US and Israel providing expertise.
Greece officially asked for the alliance's help after the March 11 train bombings in Madrid killed close to 200 people, in an attack linked to the Al-Qaeda network of Osama bin Laden.
Greek officials sought swiftly to blame home-grown groups for Wednesday's attacks.
"From the facts evaluated so far, it is becoming clear that the action comes from domestic, extremist elements without particular capabilities and perspective," said Greek Public Order Minister Yiorgos Voulgarakis from Washington, where he is on a three-day visit.
"There is absolutely no reason to link this incident with the Olympics. It is a local affair," a senior police official told AFP on condition of anonymity.
But Bob Carr, the premier of Australia's New South Wales state which hosted the 2000 Sydney Olympics, said the attacks were a cause for serious concern.
"Even if it's established it's not Al-Qaeda, even if it were established it's not an international terrorist group, it would still be very, very worrying of course," Carr said.
Athens is putting the final touches to security arrangements which will cost 650 million euros (780 million dollars), and involve more than 50,000 police officers and soldiers.
Security is the number one priority of Athens organisers, with a tense international situation in the Middle East and Iraq increasing the threat of attacks during the Games.
The Games fell victim to extremist attacks in Munich 1972, where 18 people - 11 of them Israeli athletes - were killed in a hostage-taking and Atlanta 1996, when a bomb in a park claimed two lives.
No one has yet claimed responsibility for Wednesday's attack, and police are investigating links to local extremist groups, which they say do not have the capacity to stage a major assault.
A foreign security expert expressed concern over the attack. "One hundred days before the Games, such attacks do note augur well," the expert said on condition of anonymity.
The Australian Olympic Committee (AOC) also voiced concern, but said it was not contemplating pulling its team out of the Games.
"Any bomb that goes off in Athens is worrying," said AOC secretary general Bob Elphinston. "This (Athens) is now the Olympic city and again whether it's a coincidence that it's 100 days to the Games... time will tell."
Britain's top Olympic official Craig Reedie warned Athens over their security measures.
"There are no options. They simply have to get security as right as humanly possible," Reedie said, adding the issue was bound to be raised at a meeting of the European Olympic Committee in Belgrade on Friday.