Thousands of people have marched in Bosnia to protest against a Mass being held to honour Croatia's Nazi collaborators and civilians killed after World War II.

The annual service, usually held in Austria at the site of the Croatian regime's last stand, was moved to Sarajevo because of coronavirus restrictions in Austria.

Croatian groups gather each year for the commemorations, co-organised by the Catholic Church in Bosnia and Croatia, often brandishing Nazi memorabilia.

The Nazi-hunting Simon Wiesenthal Center urged the Bosnian government to ban the Mass, labelling it a "travesty of memory and justice".

The service provoked outrage from most political parties, Jewish leaders, the Serbian Orthodox Church and anti-fascist NGOs, who held a march during the Mass in central Sarajevo.

"In Sarajevo, a multi-ethnic and anti-fascist city, there is no room for fascism," local Jewish leader Boris Kozemjakin, who took part in the march, told AFP.

Sarajevo Archbishop Vinko Puljic, who held the Mass in the Bosnian capital's cathedral, earlier rejected the accusations and said praying for victims' souls did not mean approval of their acts.

"No one has the right to neglect the victims for whom we pray today," Archbishop Puljic said during the Mass.

"We want that double standards in respecting the victims of hatred and massacre be stopped."

Meanwhile, the marchers, who rallied despite a ban on public gatherings during the coronavirus pandemic, sang songs linked to the anti-Nazi struggle.

"Death to Fascism, Freedom to People!" they chanted.

Above a monument with names of 55 people from Sarajevo killed by the Croatian fascist regime known as Ustasha, the organisers of the march placed a large photo showing the hanged victims.

Large banners reading "I'm an anti-fascist too" were also placed at the main Titova street.

The service was held under tight security and police sealed all roads leading to the cathedral with metal fences.

Only about 20 people attended the service which, like the march, ended without incident.

The Mass, originally announced as the service for those killed at Bleiburg, was eventually presented as the one for "all war and post-war victims".

The Ustasha persecuted and killed hundreds of thousands of Serbs, Jews and anti-fascist Croatians.

At the time, the so-called Independent State of Croatia (NDH) included Bosnia and parts of Serbia.

More than 10,000 Sarajevo residents - mostly Jews but also Serbs and Roma - were killed by the Ustasha regime during WWII.

Near the end of the war, the Ustasha, accompanied by civilians and Slovenian and Serbian collaborators, started to flee towards Austria hoping to surrender to British forces.

But the British refused their surrender.

The Ustasha were caught and executed by Josip Broz Tito's partisans in the border region between Austria and Slovenia.

Croatian conservative Prime Minister Andrej Plenkovic said earlier that 75 years on "we remember a difficult chapter of Croatia's history and we remember all the victims". 

The number of those killed in the Bleiburg area - where the commemorations are usually held - is still debated but independent historians put it at tens of thousands.

Short memorial ceremonies for the victims were also held in Croatia.