The protests followed the murder of left-wing activist Bjorn Soderberg, 41, who was shot in the head in Stockholm a week ago.

In Sweden's biggest anti-racist demonstration to date, at least 6,000 people in central Stockholm listened to speeches from labour union leaders calling for an end to right-wing extremism.

"People are in deep shock. We haven't had this kind of violence in Sweden before," said Maria Paz Accardeo, responsible for ethnic integration at Sweden's LO Trade Union Federation.

Three Swedes linked to neo-Nazi groups were charged with Mr Soderberg's murder on Monday. He was believed to have received threats after his complaints forced a fellow worker, a neo-Nazi, out of the union.

'It has to stop'

A bomb exploded outside a union office in Gavle, near Stockholm, on Friday night in an apparent sign of extremist anger at the nation-wide demonstrations.

No-one was hurt in the blast, the latest of a number of neo-Nazi attacks in the past year.

"People have been saying for too long that these extremist groups are just a handful of youths - but it is very serious," said Maria Lofberg, a 31-year-old ceramics artist at the demonstration.

Mr Soderberg's murder has rekindled a national debate on how to clamp down on extremists.

Police shot, journalist bombed

In June, a journalist who documented the white supremacist movement in Sweden was seriously injured when a bomb exploded as he opened his car door.

A month earlier, two neo-Nazis were charged with shooting dead two policemen after a bank robbery.

So far, Swedish authorities have backed away from calls to outlaw the extremist groups but have demanded stronger action by police.