(LUXEMBOURG) - The European Union signed up to closer ties with Serbia on Tuesday, moving it closer to EU membership despite disputes over Kosovo's independence and Belgrade's failure to catch war criminals.

Serbian Deputy Prime Minister Bozidar Jelic and EU foreign ministers gathered in Luxembourg signed the pact, which the Europeans hope will boost the chances of pro-Europe forces over nationalists in elections there next month.

Pro-Western groups in Serbia took to the streets of Serbian cities within moments of the signing, waving pro-European placards and honking car horns as the flags of the EU and Serbia fluttered from windows.

Serbian Foreign Minister Vuk Jeremic said the signing of the deal marked "a historical day for Serbia and for the EU."

"We believe we are irreversibly on the road to EU membership," he told reporters.

Slovenian Foreign Minister Dimitrij Rupel, whose country holds the EU's rotating presidency, signed the text with Jelic and EU Enlargement Commissioner Olli Rehn, under the gaze of Serbia's pro-Europe President Boris Tadic.

EU foreign ministers also took turns to sign the Stabilisation and Association Accord (SAA), a first step towards membership of the European bloc.

Most EU nations wanted to sign the SAA, primarily to boost Serbia's pro-European parties ahead of a general election on May 11.

EU ministers had worked through the night trying to persuade Belgium and the Netherlands to drop their staunch opposition to signing the pact.

The two had insisted that Belgrade had to first fully cooperate with the UN war crimes court by handing over suspects, chief among them former Bosnian Serb army chief Ratko Mladic.

Mladic -- along with the Bosnian Serb war-time political leader Radovan Karadzic -- has been charged with genocide, war crimes and crimes against humanity over the 1995 massacre of 8,000 Bosnian Muslims in Srebrenica.

To overcome the objections it was agreed that the SAA would not be ratified by the 27 member states, and therefore not enter into force, until Belgrade cooperates sufficiently with the UN war crimes court.

Jeremic denied the deal with the EU was purely symbolic.

"This is not an empty shell, this is an important political step," he said.

Tadic and Jeremic had persistently called for the accord to be signed before Serbian legislative elections to boost their chances of prevailing over nationalist Prime Minister Vojislav Kostunica.

The Serbian nationalists have been incensed by the fact that most EU nations have swiftly recognised the February declaration of independence of the breakaway Serb province of Kosovo.

In Belgrade, Kostunica said Tuesday that Serbia's parliament would "annul" the pact with the European Union after the elections next month.

"The new government and the parliament of Serbia will immediately annul Tadic's illegal signature," he said in a statement.

"We will never allow anybody to sign for the independence of Kosovo in the name of Serbia and that is why today's signature is not worth anything."

Tadic opposes Kosovo's independence but not at the expense of Serbia's EU integration.

General Affairs and External Relations Council (GAERC), 28-29 April 2008

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