Serbian police have announced the arrest of a former aide to the fugitive Bosnian Serb wartime commander, General Ratko Mladic.
Ratko Mladic's whereabouts are still unknown
Sasa Badnjar is suspected of helping the general to evade capture.
He was part of Gen Mladic's security team during the Bosnian war in the early 1990s.
Nato troops have also searched the eastern Bosnian home of Milisav Kljestan, another alleged aide to Gen Mladic. The raid happened in Vlasenica.
Mr Badnjar was picked up on Monday, when the UN's chief war crimes prosecutor Carla del Ponte was in Belgrade, urging the authorities to capture Gen Mladic.
The international war crimes tribunal is anxious to put Gen Mladic and the Bosnian Serb political leader, Radovan Karadzic, on trial to face war crimes charges, including genocide.
Last month the Serbian police arrested another of Gen Mladic's suspected aides, the former Bosnian Serb lieutenant, Jovo Djogo.
Correspondents say the arrest last year of Croatia's top fugitive war crimes suspect, General Ante Gotovina, was preceded by the detention of several of his aides and supporters.
Gen Mladic commanded the Bosnian Serb armed forces and is wanted for his involvement in the siege of Sarajevo and the massacre of nearly 8,000 men and boys at Srebrenica in 1995.