Ratko Mladic, the Bosnian Serb wartime commander, has been confronted with video and documentary evidence that he personally ordered the killing of up to 8,000 Muslim men and boys from the town of Srebrenica in July 1995.

The 70-year-old former general has denied the charges, claiming he was visiting Belgrade for official meetings and a wedding while the Srebrenica massacre took place. However, the prosecution at the international criminal tribunal for the former Yugoslavia demonstrated that Mladic was in Srebrenica and the surrounding towns on the critical days from July 11 to 14 when the Muslim enclave fell to his forces, and when men and teenage boys were rounded up and separated from women and children before being killed.

"This was not an army out of control or under the control of someone else. Only an army strictly under the control from the top could have murdered over 7,000 people in four days," said Peter McCloskey, one of the trial prosecutors.

"The VRS [the Republika Srpska army] carried out orders with incredible discipline, organisation and military efficiency … It was truly amazing feat of utter brutality."

After the prosecution's opening statement, the judge announced the trial would be delayed because the prosecutors had failed to turn over all their documentary evidence to the defence. Defence lawyers said that up to 1m pages of documents had not been handed over and demanded a six month-delay.

The prosecution admitted that it had failed to hand over 37,000 documents, each of multiple pages, of witness statements and other evidence. Prosecutors declared they had handed over the evidence in November, but only realised on Friday that they had not in fact done so.

Judge Alphons Orie said: "The chamber is still in the process of gathering information of the scope and full impact of this error."

The Dutch judge added that he would announce a new start date for the prosecution's presentation of evidence and witnesses "as soon as possible".

Tribunal sources said the judge was unlikely to grant the six-month delay demanded by the defence but would agree to some delay, of a couple of months at most.

The tribunal has already been criticised for the slow pace of its trials. The trial of the former Yugoslav president Slobodan Milosevic took five years and ended only with his death from a heart attack in March 2006. Mladic's trial is expected to last at least four years.

Mladic himself listened impassively to the evidence presented against him. He became animated only once, clapping and giving a thumbs-up sign when a video was shown of him interrogating and shouting at the Dutch UN commander, Thom Karremans.

His troops were supposed to protect the Srebrenica enclave, but were hopelessly outnumbered.

Again and again, Mladic asked Karremans if his soldiers had fired on Bosnian Serb troops who had overrun Srebrenica, and demanded to know if Karremans had called in Nato air strikes.

Karremans insisted that UN soldiers had orders to shoot only in self defence and that air strikes were decided by the UN headquarters in New York.

In fact, as McCloskey pointed out, the air strikes were too little, too late to stop the Serb capture of the enclave and the deaths of the men and boys. Women, children and old men were meanwhile bused to Muslim-held territory in northern Bosnia.

The tribunal was shown video footage of Mladic walking through Srebrenica town on 11 July 1995, just after it had fallen.

He tells an interviewer: "We give this town to the Serb people as a gift … Finally the time has come to take our revenge on the Turks [referring to Muslims] in this region."

The prosecution also showed video footage of Mladic at the scene while men and boys were separated from their families. Film was also shown of the operation to round up men and boys who had tried to escape through the woods, and of piles of corpses outside a nearby warehouse. Other documentary evidence included Mladic's written order to provide several tonnes of diesel fuel to a Bosnian Serb officer in Zvornik whose job was to excavate mass graves and rebury the remains of the victims in smaller graves in an effort to avoid detection.

Speaking after the morning hearing, Hatidza Mehmedovic, whose two sons and husband were killed in the massacre, said that despite the evidence of what happened, the international community was still conniving in the continuing "ethnic cleansing of the area".

She pointed to a change in municipal law in Srebrenica earlier this month, accepted by the international community, which meant that Muslim survivors of the massacre could not vote for the mayor. The change is likely to lead the municipality to come under Serb control in elections in October.

"What is even worse is that the whole world is seeing this and even now is not doing anything about it. The [ethnic cleansing] project is still alive. People are still suffering. Crimes are being rewarded," Mehmedovic said.

"Families of those who were killed cannot vote. With this law, they are legalising genocide. This is very dangerous for the region. This is what has to be stopped."

Mehmedovic added: "Nothing more can happen to me, but I don't want any other mother anywhere to be in my shoes and go looking for the bones of their children, and be happy if find only small bones. With my elder son, they have only found two bones. With my younger they have almost a full skeleton. This has to be a fight for justice so that no mother has to look for their children in mass graves."