This is a sad day for Serbia, and not one but one hundred steps back for human rights in this country," said Jovanka Todorovic, one of the gay pride parade organisers.

On Friday, Serbian authorities banned the gay pride parade and a number of counter protests because of security concerns.

It is the second time in three years that a gay pride parade is unable to go ahead in Serbia because of threats by ultra-nationalists. Several extremist organisations had called for anti-parade protests on Saturday and Sunday, which are now also banned.

In 2010 Serbia held its first gay pride in ten years but violent riots followed. More than 150 people, mostly police officers, were wounded in clashes between security forces and ultra-nationalists and hooligans, which caused substantial damage to the centre of Belgrade.

"This is a defeat for all citizens of Serbia: today, it's the gays, tomorrow, God knows which minority group," organiser Goran Miletic told reporters.

But the activists pledged to keep on with preparations for the pride parade in 2012, while indicating they might take legal measures against the state before the European Court of Human Rights in Strasbourg.

"This is the least we can do in order to protect our constitutional rights before justice... And we are ready to prepare and organise the pride next year," Miletic said.

Instead of marching, the activists briefly halted traffic in a central Belgrade avenue by spreading a pink banner saying "Love, normally," and pouring cans with so-called "rainbow" paints on the street.

No incidents were reported during the brief performance, while police stood by.

Amnesty International said the Serbian authorities' decision to ban the pride was a "dark day for human rights."

"The Serbian authorities... have bowed to pressure from right-wing groups who have failed to understand or respect the rights to freedom of expression set out in the Serbian constitution and law," the group said in a statement.

"Instead of rainbow flags in Serbia, it is a dark day for human rights," it added.

The ban on the pride march "violates the Serbian government’s obligations to guarantee freedom of expression and assembly... (It) undermines the right to non-discrimination," the group said.