The chief U.N. war crimes prosecutor for the former Yugoslavia left open for the first time Monday the possibility that Europe's most wanted fugitive, Ratko Mladic, may be hiding outside Serbia.

The prosecutor, Serge Brammertz, said Serbia remains responsible for arresting Mladic, the wartime Bosnian Serb army commander, who is wanted for genocide. Mladic has been on the run since 1995.

Brammertz said the clues to finding him, wherever he is, lie in Serbia.

"Our main working hypothesis is still that the answer and the leads to his arrest are in Serbia," Brammertz said. "But, of course, the operational activities are not only concentrated on Serbia."

"We can never exclude any working hypothesis," Brammertz said.

He urged authorities to focus on Mladic's support network.

"It is obvious that he is not alone and it is obvious that he has the support of other persons," Brammertz said. "He is a professional, he has worked long enough in the operational services to know how to hide and how to take counter measures against investigative approaches," he told reporters in Belgrade, the Serbian capital.

Brammertz plans to report to the U.N. Security Council next month on how serious Serbia is about apprehending Mladic and another fugitive, former Croatian Serb leader Goran Hadzic.

Brammertz' assessment of how well Serbia is cooperating with the Netherlands-based U.N. war crimes court will be a crucial consideration for the European Union as it decides whether to allow Serbia to move closer to membership.

Brammertz said that there have been improvements in Serbia's performance, but "we are not there yet."

"There is more that can be done and more needs to be done," he said.

Serbian President Boris Tadic said after meeting Brammertz that "Serbia will continue to do whatever it can to locate, arrest and extradite" Mladic and Hadzic to the U.N. tribunal.

Brammertz sharply criticized Serbia recently for its failure to find the fugitives. He said the wanted men are "within reach" of Serbian authorities, something Serbian officials denied vehemently. They suggested Mladic could be out of the country.

An alleged former close associate of Mladic said in a recent interview with a Belgrade newspaper that Mladic is probably hiding in Russia. There has been no official reaction from Russia or Serbia to the claim.

Mladic is wanted by the U.N. court for the killing of 8,000 Muslims in Srebrenica in 1995 — the worst atrocity in Europe since the end of World War II — and the three-year shelling and siege of Sarajevo during Bosnia's 1992-95 war.


Associated Press writer Dusan Stojanovic contributed to this story.