The BBC's Mark Devenport: ''Mr Annan said the massacre would haunt the UN forever''

An estimated 7,000 men and boys were slaughtered in the so-called UN ''safe area'' after the Bosnian Muslim town was overrun by Serbs.

In his report, UN Secretary-General Kofi Annan said ''safe areas'' should never be established again without credible means of defence.

And he said UN peacekeepers should never be deployed again where there is no ceasefire or peace agreement.

His 155-page report said the UN Security Council should have approved "more decisive and forceful action to prevent the unfolding horror".

"Not since the horrors of World War II had Europe witnessed massacres on this scale," Mr Annan added. "The tragedy of Srebrenica will haunt our history forever."

Cardinal lesson

Mr Annan said observers had been quick to blame the Dutch UN battalion which withdrew from Srebrenica in the face of Serb attack.

But he pointed out that the Dutch commander's repeated requests for the use of air power were turned down.

The then Bosnian Serb leader Radovan Karadzic faces war crimes charges, if arrested

Mr Annan said the UN was wrong to declare it would only use Nato air power against the Serbs as a last resort.

"The cardinal lesson of Srebrenica is that a deliberate and systematic attempt to terrorise, expel or murder an entire people must be met decisively with all necessary means, and with the political will to carry the policy through to its logical conclusion," he added.

Mr Annan criticised the Security Council, staff at the UN headquarters including himself, UN peacekeepers in Srebrenica, and the six-nation "Contact Group" that oversees the Balkans.

But he said primary responsibility lay with wartime Bosnian-Serb leader Radovan Karadzic and his military chief General Ratko Mladic, who planned the systematic killings.

Both men have been indicted by the international war crimes tribunal but are still at large.

Shot in the head

The remains of around 2,500 people have been found in mass graves. Thousands more who are still missing will probably be found in other burial sites, Mr Annan said.

Many of those exhumed had their hands bound or were blindfolded. Some were shot in the back, others in the head.

Mr Annan said the fall of Srebrenica was ''shocking" because the enclave's inhabitants had believed the UN and Nato would ensure their safety.

Yet Serb forces ignored the Security Council, pushed aside the UN troops and overran Srebrenica with ease.

Mr Annan said military force should have been used to halt the killings.

"Many of the errors the United Nations made flowed from a single and no doubt well-intentioned effort: we tried to keep the peace and apply the rules of peacekeeping when there was no peace to keep," he added.