By Malcolm Brabant
BBC News, Athens
The blast has been blamed on a leftist militant group
A small bomb has exploded outside the Greek parliament in one of the busiest areas of the capital, Athens.
The blast blew out some of the parliament building's windows but no-one was injured in the attack, blamed on left-wing militant groups.
Police were able to clear the area around the building after receiving a 15-minute warning ahead of the blast.
The bomb was placed in a rubbish bin close to the Tomb of the Unknown Soldier, in Constitution Square.
Ceremonial guards protecting the tomb refused to leave their posts.
The attack is likely to be the work of one of a number of domestic militant groups, spawned after the riots of December 2008.
Their anti-establishment campaign has recently changed direction to retaliate against the socialist government's austerity measures, aimed at resolving Greece's economic crisis.
Though the attack may have caused little physical damage, it will trouble international financial experts monitoring Greece.
Ratings agencies have warned they will downgrade the country's credit-worthiness again if there is social unrest or if the government fails to persuade the country to accept a programme of cuts.
The bombers' message could not have been clearer - especially as parliament was sitting at the time - they were saying they could strike with impunity against one of the most heavily guarded buildings in the country.