Oric is a hero for Muslims in eastern Bosnia

His warning came as Nato-led forces seized the former commander of Muslim military units in the region of Srebrenica, Naser Oric, and transferred him to the UN war crimes tribunal in The Hague.

"There is no place to hide for anyone accused by the tribunal of these horrific crimes," Lord Robertson said in a statement.

"You have only two choices: turn yourself in with dignity, or justice will be brought to you.

"The net is closing."

The arrest follows a major crackdown in Serbia on criminal gangs and supporters of the former Yugoslav President Slobodan Milosevic, some of whom are accused of masterminding the murder of Serbian Prime Minister Zoran Djindjic.

More than 2,000 people are being held, including some who may now be handed over to the war crimes tribunal.

Civilian deaths

Mr Oric was seized in Bosnia, near the town of Tuzla on Thursday night.

A secret indictment from the tribunal enabled the Bosnian Stabilisation Force (S-For) to make a surprise arrest.

General Mladic used to be sheltered by the Yugoslav military

He is charged with "violations of the laws or customs of war, to include murder, cruel treatment, wanton destruction and plunder".

Bosnian Serbs say he was responsible for the murder of more than 1,000 Serb civilians in villages near Srebrenica during the 1992-1995 war.

However he is a local hero to many Muslims in eastern Bosnia, where his image is a common sight on posters.

Mr Oric led the defence of Srebrenica against Serb forces, but left before they overran the town in July 1995 and proceeded to massacre thousands of its Muslim inhabitants.

Networks under pressure

Mr Karadzic and General Mladic are accused of genocide, war crimes and crimes against humanity for the persecution of non-Serbs in Bosnia.

Mr Karadzic is thought to be hiding in remote eastern Bosnia or in his native Montenegro.

General Mladic has in the past been reported to be living in or around Belgrade, under the protection of influential groups in the Serbian military.

The top international envoy in Bosnia, Paddy Ashdown, said on Wednesday that networks supporting the two fugitives were under "extreme pressure".

He said raids in Bosnia last month aimed at crippling the Karadzic support network had yielded "a vast amount of information".