Members of the human rights' organisation SOS-Mitmensch held an all-night vigil at the site of the wartime Nazi Gestapo headquarters in Vienna and on steps leading to the city's oldest church, the Ruprechtskirche, over the weekend.
Two groups of skinheads shouting racists slogans kicked and stamped on scores of candles placed on the steps leading to the church in the early hours of yesterday, the Austrian news agency APA quoted activists as saying.
SOS-Mitmensch said its members immediately called the police, but none arrived until later in the morning.
The vigil began hours after the four gypsies, all Austrian citizens, were buried in their home town of Oberwart 60 miles south of Vienna.
President Thomas Klestil, most of the Austrian cabinet and other politicians, joined 2,000 mourners at the funeral.
The four had been lured by a racist sign outside the town saying "Romanies back to India" and were killed by a booby-trap bomb.
A right-wing extremist group, calling itself the Bavarian Liberation Army, claimed responsibility for the attack and for a second bomb which exploded two days later in the nearby village of Stinatz, injuring a workman.
Stinatz is inhabited mostly by ethnic Croats, many of whom fled former Yugoslavia when war broke out in Croatia in 1991.
Interior Minister Franz Loeschnak said yesterday that telephone bugging would be used against the extremists. Mr Loeschnak has come under increasing criticism for failing to tackle race-related incidents, all believed to be the work of neo-Nazis activists, since 1993, when letter bombs were sent to ethnic citizens. No one has been caught over either incident.