People holding flowers and a Greek flag stand near the local offices of far-right Golden Dawn party, following last night's shooting, in a northern suburb of Athens November 2, 2013. REUTERS/John Kolesidis

By Renee Maltezou

ATHENS (Reuters) - A brazen drive-by shooting that killed two young members of Greece's far-right Golden Dawn party has shocked Greeks and prompted soul-searching about whether the crisis-hit country is slipping into a "cycle of violence".

Greece's anti-terrorism force is investigating whether Friday's rush hour shooting outside the party's offices in Athens was retaliation for a fatal stabbing of an anti-fascism rapper by a Golden Dawn supporter in September, police said.

Rapper Pavlos Fissas's death sparked protests across Greece and a government crackdown on Golden Dawn, which is widely considered neo-Nazi and is blamed for attacks against migrants.

"We cannot let this cycle of violence continue," Makis Voridis, a senior lawmaker in Prime Minister Antonis Samaras's New Democracy party, told Mega TV. "This must end here."

"Twelve bullets against democracy," top-selling daily Ta Nea wrote on its front page on Saturday. "The double cold-blooded murder was a coarse provocation against stability."

The two Golden Dawn supporters, aged 22 and 27 years old, were gunned down in a busy street during the evening rush hour. A third man was seriously injured in the chest and stomach and doctors said he remained in a critical condition.

According to witnesses and CCTV camera footage, the attacker, who had an accomplice, got off a motorbike and shot the victims at close range, police said. Twelve bullets were found at the crime scene from a 9 mm gun.

No one has so far claimed responsibility for the attack.

"The target, the place and the time of the attack are symbolic," said Mary Bossis, professor of international security at the University of Piraeus.

"This act had an audience and those behind it have succeeded in sending the message they wanted."

Golden Dawn, Greece's third most popular political force, urged Greeks to join a memorial service on Saturday evening outside its offices in the northern suburb of Neo Iraklio. Residents began gathering at the site and lay flowers.

INSTABILITY

Politicians who have in the past queued up to pour scorn on Golden Dawn united in condemning the shooting.

"This murder creates a climate of instability and targets democracy," said the leftist Syriza party.

Greece is in the sixth year of a recession that has fuelled anger against its foreign lenders and the political class, blamed by Greeks for bringing the country close to bankruptcy.

Golden Dawn, which rejects the neo-Nazi label but uses a swastika-like emblem and its leader has denied the Holocaust, stormed into parliament last year on an anti-immigrant agenda.

Since Fissas' killing, the party has seen several of its members arrested as part of an investigation into accusations it has been involved in a wave of attacks and crimes. Golden Dawn has denied any wrongdoing and said it had asked for police protection at its offices after receiving threats.

The Greek government has in the past promised to wipe out a party it describes as a "neo-Nazi gang". On Friday, it vowed to bring the killers of the two Golden Dawn supporters to justice.

Small-scale bomb attacks against police, politicians and businessmen are frequent in Greece, which has a history of leftist violence. A prominent fatal shooting like Friday's attack was last seen in 2010, when a Greek journalist was shot dead outside his home.

"Yesterday's killing marked a continuation of political uncertainty and instability in the country," said George Tzogopoulos, analyst at the Athens-based ELIAMEP think-tank.

"These kinds of killings, in the span of only 40 days, are obviously worrying for a country that is the cradle of democracy."

(Additional reporting Deborah Kyvrikosaios; Editing by Deepa Babington and Gareth Jones)