BELGRADE, Serbia » Thousands of Serbian riot police have cordoned off central Belgrade for a gay pride march amid fears of attacks from extremists in the predominantly conservative Balkan country.

Helicopters flew above the downtown area which was sealed off for traffic early Sunday, hours before the planned start of the gathering.

Authorities have cancelled several pride events in the past after massive clashes with extremists in 2010 when more than 100 police and extremists were injured.

Serbia has since sought to boost gay rights as part of its bid to join the European Union, including appointing an openly gay minister in the current government.