Fugitive former Bosnian Serb military commander Ratko Mladic is in Serbia and should be arrested by the end of the year, chief U.N. war crimes prosecutor Carla del Ponte said on Tuesday.

She said Mladic, wanted on genocide charges over the 1995 Srebrenica massacre of about 8,000 Muslims, was probably moving around more than in the past because the recently appointed Serbian government is seriously trying to arrest him.

"Mladic is in Serbia because all the indications we have from the authorities, also in Serbia, are that he's there," she told a news conference at the European Policy Centre after talks with EU Enlargement Commissioner Olli Rehn.

Mladic was avoiding using mobile or fixed telephones after fugitive former Croatian general Ante Gotovina was located in the Canary Islands in 2005 after a cell phone call with his wife was intercepted by Croatian security services, she said.

That evidence, presented to her by Croatian Prime Minister Ivo Sanader, enabled the prosecutor to give the European Union the green light to open membership talks with Croatia.

Del Ponte repeated her plea to the EU not to sign an agreement on close relations with Serbia, currently under negotiation, before Mladic was handed over to the Hague International Criminal Tribunal for former Yugoslavia.

She confirmed that she had agreed to stay on an extra three months until the end of this year, partly in the hopes of bringing the four remaining indicted fugitives to justice before her term expires.

She said she had no current information on the whereabouts of former Bosnian Serb political leader Radovan Karadzic and was concentrating for the moment on bringing in Mladic.

"I don't know where Karadzic is. Since months we have received no information. Last year we received some information that he was in a monastery in Montenegro," she said.

"We will get him because we are not forgetting him."

Former Bosnian Serb General Zdravko Tolimir refused to enter a plea at the Hague tribunal on genocide charges on Tuesday and demanded an inquiry into the circumstances of his arrest, saying he had been illegally kidnapped and transferred from Serbia to Bosnia.