Serb nationalists have rallied against NATO in Belgrade, ahead of an international military conference.

Angry protesters burned NATO flags and carried banners denouncing the military alliance.

Leaders of the Serbian Radical Party, which organized the protests, called President Boris Tadic a traitor and urged him to resign. A group of at least 100 radicals gathered outside the presidential office and tried to deliver a letter to Mr.Tadic in which they accused him of having thrown Serbia “on its knees” before Brussels and Washington.

The deputy head of the party, Dragan Todorovic, said it was unacceptable to allow into Serbia those who had thrown bombs on it. NATO air forces bombed Belgrade in 1999 to halt its crackdown on ethnic Albanian separatists in Kosovo.

President Tadic said Monday that protests are an acceptable part of the democratic process.

Serbia is hosting the international military conference in Belgrade this week. Participants in the conference will be the top military representatives from NATO countries and their partners. While not a member of NATO, Serbia does belong to the alliance's Partnership for Peace, a program of bilateral cooperation between members and NATO.

The Serbian government is hoping to set a date for the start of negotiations with the European Union for Serbia's membership in the block. It got closer to that goal after delivering a top war crimes suspect, Bosnian Serb wartime commander Ratko Mladic, to the international war crimes tribunal last month.

Serbian nationalists are angry about Mladic's extradition. The former general is facing charges of genocide against some 8,000 Bosnian Muslims, but is seen as a heroic defender of Serbian interests by his supporters.