Hundreds of police were on the streets of Belgrade Saturday after authorities banned Gay Pride for the third year running, an act the EU said was regrettable.
Hundreds of police in full anti-riot gear surrounded a park in downtown Belgrade where the parade was due to take place, as well as main buildings and key crossroads.
On Friday Serbian Prime Minister Ivica Dacic announced the parade would have to be cancelled after far-right groups threatened protests.
The European Union said it expected Serbia to probe the threats of violence and "take necessary measures" to prevent them in future.
But it said the decision to ban the parade was regrettable. "It is a missed opportunity to show respect for fundamental rights," EU Enlargement Commissioner Stefan Fuele said in a statement.
"I am committed to seek from candidate countries that they fully embrace values such as freedom of assembly and freedom of expression that are amongst the core foundations on which the European Union project is built," Fuele said.
"This is particularly important in the context of Serbia's accession negotiations," he added.
Serbia, a candidate for EU membership since mid-2012, is expected to start accession talks with Brussels in January, but human rights activists have already warned it could be hampered by the ban of the pride.
Following the news of the ban a few hundred people gathered outside the Serbian government building late Friday carrying a large banner that read: "This is pride".
Escorted by dozens of police in anti-riot gear, the group then marched through downtown Belgrade to the Serbian parliament building, holding a huge rainbow-coloured flag.
The last Gay Pride parade in Serbia in 2010 ended in violence. Over 150 people were injured, mostly police, and the damage estimated was more than one million euros ($1.35 million).