Del Ponte insisted Karadzic and Mladic must be arrested

"It will be made public only when we provide it in the court," Ms Del Ponte said in the Bosnian capital, Sarajevo.

She spoke at the end of a tour of the Balkans ahead of a report she is to give to the UN Security Council.

A tape shown this week at the trial of former Yugoslav President Slobodan Milosevic has shocked many Serbs.

It depicted Serbian paramilitaries killing Muslim civilians and led to 11 arrests in Serbia and Bosnia.

Reaction to the video across the former Yugoslavia has been swift and strong, says the BBC's Matt Prodger in Belgrade.

One Bosnian mother turned on her television to watch the news and was shocked to witness her 16-year-old son being murdered 10 years ago.

On the streets of Serbia, where many people have refused to believe the massacre ever happened, reactions were split between horror and disbelief, our correspondent says.

"The impact in Belgrade was a shock," said Ms Del Ponte.

I need Karadzic and Mladic in The Hague before 11 July to be able to participate in the commemoration of Srebrenica Carla del Ponte

"I think that the attitude was changing before that. It was just another element that can motivate it to full co-operation with us," the chief prosecutor said.

But now she wants results, our correspondent says - not least the arrest of the two men charged with genocide over Srebrenica - Bosnian Serb leader Radovan Karadzic and his military commander, General Ratko Mladic.

"I need Karadzic and Mladic in The Hague before 11 July to be able to participate in the commemoration of Srebrenica," she said.

That was "the only decent way to pay tribute" to those who lost fathers, sons and husbands in the massacre.

Her visit comes ahead of a report to the UN Security Council on co-operation by Serbia and Montenegro, Bosnia and Croatia with the Hague tribunal.

Eventful time

Our correspondent says that, with the Serbian arrests, Ms Del Ponte's latest visit to the region has attracted even more attention than usual.

Ratko Mladic and Radovan Karadzic have evaded capture for years

And it has been an eventful six months since she last reported to the Security Council.

Serbia and Montenegro have surrendered more than a dozen war crimes suspects, the Kosovan prime minister has resigned to stand trial for alleged war crimes, and Croatia's EU membership talks have stalled as a result of failure to arrest a key fugitive, Ante Gotovina.

But there is still no sign of the two men most sought by the prosecutor.