BELGRADE, Oct 30 (Reuters) - The son of Bosnian Serb war crimes suspect Ratko Mladic is being questioned by Serb police seeking information about the whereabouts of his fugitive father, Serb officials said on Tuesday. Extraditing the elusive general to the United Nations war crimes tribunal is the European Union's main condition for allowing Serbia to advance to the first stage of EU membership.

On a visit to Serbia last week, chief tribunal prosecutor Carla del Ponte said Belgrade should not be allowed to have closer ties with the EU until Mladic is handed over.

Mladic's son Darko "is not arrested or detained, but answered a police call to give information," said Rasim Ljajic, the Serbian official dealing with the Hague tribunal.

The questioning could last up to four hours, Ljajic added in a statement to state news agency Tanjug. The ultranationalist Radical Party earlier told the Serbian parliament that Darko Mladic and his wife were arrested on Monday.

Mladic, the commander of the Bosnian Serb army in the 1992-95 Bosnia war, was indicted by the Hague tribunal for the July 1995 Srebrenica massacre of 8,000 Bosnian Muslims and the 43-month siege of Sarajevo.

Del Ponte says he is in Serbia, protected by hardliners in the army and security services. Serbia has admitted he lived in Belgrade until January 2006, but says it cracked down on his loyalists and is doing its best to arrest him.

In mid-October, the EU postponed a decision to initial a first agreement on closer ties with Serbia because del Ponte said Belgrade's cooperation with her court was "still too slow and not yet sufficient".

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