The UN's highest court gave its backing on Thursday to Kosovo's 2008 declaration of independence from Serbia, saying the move did not breach international law.

In a non-binding verdict, the International Court of Justice rejected Belgrade's argument that the declaration had no legal basis. Pristina hopes the outcome will lead to more nations recognising its independence.

"The court has concluded ... that the adoption of the declaration of independence of 17 february 2008 did not violate general international law, Security Council resolution 1244, or the constitutional framework," the ICJ's president Hisashi Owada told a crowded courtroom.

"The adoption of that declaration (of independence) did not violate any applicable rule of international law," he added at the court in The Hague.

While there was no immediate reaction from the governments in Belgrade or Pristina, the United States praised the verdict and asked European nations to "unite" behind it.

The verdict came after Serbia said backing for the move would imperil borders around the world and urged the court to respect its territorial integrity.

"No frontier in the world and in the region would be safe" if the court supported Kosovo's "secession", Foreign Minister Vuk Jeremic, who was in The Hague for the verdict, had earlier told the Tanjug news agency.

Sixty-nine countries have so far recognised Kosovo as independent, including the United States and all but five of the 27 EU member states. Russia, Serbia's most powerful ally on the world stage, has not.

On the eve of the hearing, the United States reiterated its support for Kosovo's independence during a meeting in Washington between Vice President Joe Biden and Hashim Thaci, Kosovo's prime minister.

Biden "reaffirmed the United States' full support for an independent, democratic, whole and multi-ethnic Kosovo whose future lies firmly within European and Euro-Atlantic institutions," a White House statement said.

The 1998-99 war between separatist Kosovo Albanians and Serbian strongman Slobodan Milosevic's security forces ended when a NATO air campaign ousted the Serbs and established a UN protectorate.

The conflict claimed several thousand mostly ethnic Albanian lives.

Landlocked Kosovo, with its two million inhabitants -- 90 percent of them ethnic Albanians -- unilaterally declared independence from Serbia in February 2008 after UN-brokered negotiations to resolve its future status failed.

The UN General Assembly, at Serbia's request, asked the ICJ in October 2008 to render a legal opinion.

Belgrade has said it wants to continue negotiations on the status of Kosovo, which it considers its southern province and the cradle of its Serbian Orthodox faith, after the ICJ verdict.

But Pristina has ruled out further status talks and expects the court to endorse its move to statehood, prompting more countries to recognise it as independent.

NATO-led peacekeepers in Kosovo were ready for violence that may meet the ruling, although they did not expect any, their German commander said.