Police sealed off downtown Belgrade on Sunday for Serbia's first gay pride parade in four years, seen as a key test of the EU hopeful's commitment to protecting minority rights.
The parade was banned the last three years after hardline nationalists attacked marchers and clashed with police at the first-ever event in 2010, leaving 150 people injured.
Following new threats by far-right groups ahead of Sunday's Belgrade Pride, several thousand anti-riot police, special police units, armoured vehicles and water cannons were deployed across the capital.
Only accredited reporters, organisers and participants wearing special bracelets were allowed to enter a large section of central Belgrade that was closed off to traffic.
Some 500 members of the ultra-nationalist Dveri group were involved in a stand-off with officers in riot gear late Saturday as they tried to march on parliament to protest the planned gay pride march.
Interior Minister Nebojsa Stefanovic urged calm ahead of the parade, warning that authorities could still stop the event if security was threatened.
The two-kilometre (mile-long) march, set to start at 1030 GMT outside the main government building, will pass by parliament before ending in front of Belgrade City Hall.
Organisers were optimistic that the parade would go ahead, saying it had been met with a warmer reception than in previous years.
"For the first time the institutions have publicly supported the organisation of the pride and media reports were more favourable for the LGBT community," one of the organisers, Boban Stojanovic, told reporters on Saturday.
Planners, who expect a few hundred people to attend the event, have released few details in advance due to security concerns.
Several foreign diplomats, including the head of the EU's delegation to Serbia Michael Davenport and European Parliament member Terry Reintke, said they would attend the march.
Some Serbian cabinet ministers also said they would join, including Jadranka Joksimovic, the European integration minister, and Culture Minister Ivan Tasovac.
Stojanovic cautiously welcomed the government's support, saying: "Only once the pride is held we will be sure that the support of the institutions was honest."
- 'Imposed' by western Europe -
Others, such as Prime Minister Aleksandar Vucic, a former ultra-nationalist who has re-branded himself as pro-European, have said they will not attend.
"My obligation is to guarantee security and safety to everybody. But my choice is not to attend the parade, no way," he said.
Tensions have been running high in highly patriarchal Serbia ahead of the event.
The head of the influential Serbian Orthodox Church, Patriarch Irinej, denounced the event as "immoral" and asked why "gay sexual orientation is right to be propagated and not paedophilia and incest".
The march had been "violently imposed by a gay lobby and their mentors from (western) Europe," he added.
Earlier this month a German LGBT rights speaker was hospitalised after being beaten in Belgrade, and several ultra-nationalist groups have announced anti-gay protests over the weekend.
Dveri members were on the streets of the capital on Saturday night while another group, Obraz, called its supporters to join a march in another central Belgrade area Sunday.
Vucic warned earlier this week that "whoever tries to provoke incidents will be very, very severely punished".
Homophobia is widespread in Serbian and other conservative Balkan societies.
Belgrade has been under pressure to improve protection for minorities, including the LGBT (lesbian, gay, bisexual and transsexual) community, since starting accession talks with the European Union this year.