(BRUSSELS) - The European Union welcomed Tuesday the arrest of former Bosnian Serb leader Radovan Karadzic but kept up pressure on Serbia's new government to track down other war crimes suspects.

European foreign ministers, at talks in Brussels, praised the arrest as a significant step for Serbia on the road to joining the EU but were cautious about whether it would unblock a key accord on closer ties.

"At last. We've been waiting for 13 years for this," said French Foreign Minister Bernard Kouchner, whose country holds the rotating presidency of the 27-nation EU until the end of the year.

"This is certainly a good thing for rapprochement between Serbia and the European Union," he told reporters.

However he cautioned: "We decide things among 27 and there are those who will say: 'OK, Karadzic is arrested, but (former Bosnian Serb military chief Ratko) Mladic is not."

Karadzic, 63, was arrested in Serbia late Monday, according to President Boris Tadic's office. Like Mladic, he is wanted for genocide over the massacre in Srebrenica in 1995, Europe's worst post-war atrocity.

The extent of Serbia's cooperation with the UN court that has indicted them -- the International Criminal Tribunal for former Yugoslavia (ICTY) -- regulates the strength of ties between Belgrade and Brussels.

The Netherlands and Belgium have so far refused attempts to ratify a Stabilisation and Association Agreement (SAA) -- a first step to joining the EU -- because of Serbia's failure to hand over UN war crimes suspects.

Dutch European Affairs Minister Frans Timmermans warned against any haste in endorsing Belgrade's fight against war criminals like Karadzic, who has been at large for 13 years.

"We need to take that step by step," he said.

"We're now waiting for Karadzic to be delivered to The Hague. Then we will look at what (ICTY chief prosecutor Serge) Brammertz will have to say on this issue," he said.

"We still have the two other suspects that need to be delivered and we need to have full clarity on that whether there is full cooperation on those issues as well."

British Foreign Secretary David Miliband also noted that other suspects were on the run, while his Swedish counterpart Carl Bildt said the arrest, while important, was only one step in a process of cooperation.

"The fact that they do it so rapidly after only a few days in office is a very significant step. Not necessarily The Step, but a step," said Bildt, once an key mediator in former Yugoslavia.

Serbia and the EU signed the SAA agreement in April but it remains on hold until Belgrade is adjudged to have demonstrated "full cooperation" with the ICTY.

That assessment must first come from The Hague-based tribunal, and then the European Commission, which supervises enlargement issues on behalf of the member countries.

The EU, having failed to stop the bloody wars in the 1990s that broke former Yugoslavia apart, has often given incentives to Serbia in an effort to foster stability in the volatile Balkans region.

But deep tensions remain between Brussels and Belgrade over Kosovo, which declared independence from Serbia five months ago in a move recognised by around 20 EU nations.

Serbia has withdrawn its ambassadors from some capitals in protest.

Meanwhile, Serbian Foreign Minister Vuk Jeremic insisted that the arrest was confirmation of Belgrade's commitment to track down those wanted by the court and to a European future.

"When it comes to the other fugitives, especially general Mladic, I can assure you that the Serbian government is going to continue doing its utmost to make sure there is full cooperation," he said.

General Affairs and External Relations Council meeting

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