European Union nations signed a pre-membership trade and aid pact with Serbia on Tuesday, signalling they want to strengthen ties with the country despite significant differences over Kosovo.

The EU's 27 foreign ministers and Serbian Deputy Premier Bozidar Djelic signed the deal.

But wary of Serbia's Balkan wars record, the EU will only implement the pre-membership deal once Belgrade fully co-operates with the Yugoslav war crimes tribunal in The Hague, which demands the extradition of the war crimes suspects.

The pact was signed after the Netherlands and Belgium lifted their vetoes on the signing of the so-called Stabilization and Association Agreement. But because the pact will not take immediate effect, the signing had a largely symbolic value.

Dutch Foreign Minister Maxime Verhagen said "the best proof" of Belgrade's co-operation with the UN tribunal would be delivering four war crimes suspects — notably Ratko Mladic, the former Bosnian Serb commander wanted for the alleged murder of 8,000 Muslim men and boys at Srebrenica in 1995 — to trial in The Hague.

At a news conference with EU officials, Serbian President Boris Tadic said he hoped the signing of the pre-membership accord will discount the impact of anti-EU parties in the run-up to the May 11 elections.

"Many enemies of our European future are engaged in scare-mongering," he added.

He vowed to quickly extradite Mladic, ex-Bosnian Serb political leader Radovan Karadzic and other suspects but said it is difficult because the suspects move around frequently.

The pre-membership accord has been on the table for months, but was put on hold after Kosovo's declaration of independence Feb. 17, which soured Serbia's ties with the EU.

 In Belgrade, Serbia's hardline Prime Minister Vojislav Kostunica declared that signing the deal was illegal and said it "cannot be interpreted as Serbia's signature for the independence of Kosovo."

EU officials insisted the EU-Serbia agreement does not apply to the territory of Kosovo, which declared itself independent from Serbia in February.