Greek police said on Sunday they had arrested two suspected guerrilla group members but a cache of weapons found in their apartments in Athens this weekend did not match guns used in recent attacks.
Police raided several houses across Greece and arrested six people aged 21-31 on Saturday, two days before the anniversary of the worst riots in decades sparked by the police killing of a teenager on December 6, 2008.
Two men arrested were suspected members of the Conspiracy of Fire Cells group, police said, adding arrest warrants had been issued against them for taking part in attacks. The other four, including a woman, were arrested for gun possession.
Seven handguns, three machine guns and three Kalashnikov assault rifles, bullets, grenades, explosives and other weapons were confiscated during the raids in Athens.
But ballistic tests showed the guns seized were not the ones used in attacks by guerrilla groups.
"The ballistic tests so far have shown that the guns confiscated are not linked to terrorism activity," the head of the Greek police, Eleftherios Economou, told reporters.
He added that other weapons found at a house in the central Greek town of Agrinio were also being tested.
Another police official had earlier said the type of weapons pointed to the Conspiracy of Fire Cells group or the Rebel Sect, who have been responsible for a series of attacks in recent years, including the killing of a policeman and a journalist.
Greece has a decades-long history of leftist violence but some groups have sprung up or become more active since the 2008 riots which paralysed Athens for weeks.
Investors will be watching this week whether protests on the anniversary of the riots will turn violent, as the Socialist government struggles with a severe debt crisis that has shaken the euro zone.
The Socialists have vowed to crack down on leftist guerrilla groups. More than 20 suspected urban guerrilla members have been arrested this year, but analysts say the groups' loose structure makes them hard to eradicate.
The Rebel Sect emerged in February 2009 in a gun and grenade attack on an Athens police station. It gunned down a policeman in June 2009 and a journalist in July this year.
The Conspiracy of Fire Cells initially staged arson attacks but turned to bombings in 2009. They claimed a wave of parcel bombs addressed to foreign governments and embassies last month.