Serbia ? A former Bosnian Serb general who is considered the third most wanted war crimes fugitive in the Balkans was arrested Thursday on the Bosnia-Serbia border, police said.

Zdravko Tolimir, indicted by the U.N. war crimes tribunal, was an aide to wartime Bosnian Serb military commander Gen. Ratko Mladic during the slaughter of up to 8,000 Bosnian Muslims in 1995 in Srebrenica – the worst single atrocity in Europe since World War II.

Olga Kavran, the spokeswoman for the chief U.N. war crimes prosecutor for the former Yugoslavia, Carla Del Ponte, said they were informed of Tolimir’s arrest by the Bosnian Serb Prime Minister Milorad Dodik.

Kavran said preparations for Tolimir’s transfer to the U.N. detention unit near The Hague, Netherlands, were under way.

Tolimir, who was reported to have organized Mladic’s escape from justice, was arrested after a major security sweep of the border region that included helicopters and anti-terrorist units, the Bosnian Serb police said.