* Killings come amid crackdown on Golden Dawn
* Attack decried across political spectrum
* Govt vows to punish "murderers" (Updates throughout)
By Karolina Tagaris
ATHENS, Nov 1 (Reuters) - Two members of Greece's far-right Golden Dawn party were killed in a drive-by shooting outside the movement's offices in Athens on Friday, raising fears of an escalation of political violence in the crisis-wracked country.
The men, both in their 20s, were gunned down at a time of growing public anger against Golden Dawn and a government crackdown on the party after the killing of a rapper in September blamed on a sympathiser of the group.
A third man was seriously wounded in the shooting on a busy street during the evening rush hour, police said, declining to go into further details.
Politicians who have in the past queued up to pour scorn on Golden Dawn - still Greece's third most popular political force - united in condemning the shooting.
"The murderers - whoever they are - will be dealt with unsparingly by our democracy. Let everyone know this," the government's spokesman Simos Kedikoglou told reporters outside the prime minister's mansion.
No one claimed responsibility for the attack. A police official, speaking on condition of anonymity, told Reuters the force suspected unnamed anti-establishment groups, and was satisfied the attack was not linked to a personal dispute.
Golden Dawn, which stormed into parliament last year on an anti-immigrant agenda, said it had asked for police protection at its offices after receiving threats.
"(Prime Minister Antonis) Samaras's anti-Greek government is to blame for the crime, which allowed out of control terrorists to murder young kids in cold blood," the party said in a statement.
The party, which rode a wave of anger against austerity imposed to cope with Greece's financial crisis, has seen several senior members arrested in an investigation into accusations it was involved in attacks and criminal activities.
The government has in the past promised to wipe out a party it describes as a "neo-Nazi gang".
Scores of police in riot gear cordoned off the streets surrounding the offices, draped with a large Greek flag, in the northern Athens suburb of Neo Iraklio, a bustling area with cafes and restaurants nearby.
Police officials, who asked not to be named, said they believed the victims were shot at close-range with a 9mm pistol.
Golden dawn uses a swastika-like emblem and its leader has denied the Holocaust, though it rejects the neo-Nazi label.
Dimitris Papadimoulis, a lawmaker from the leftist opposition Syriza party which has fiercely opposed Golden Dawn, called the shootings a "blow to democracy".
"It feeds fascism, it does not beat it," he wrote on Twitter.
Greece's public order minister, Nikos Dendias, said he would not allow Greece to become "anyone's battlefield for settling scores".
Fears of rising political violence in crisis-hit Greece also flared earlier this year in January, when unidentified attackers opened fire on the Athens headquarters of the co-ruling New Democracy party with a Kalashnikov assault rifle. (Additional reporting by Harry Papachristou, editing by Deepa Babington and Andrew Heavens)