Ban Ki-moon said on Thursday the UN was failing in its duty to protect Syria's civilians as he paid a landmark visit to Srebrenica, the scene of Europe's worst massacre since World War II.
Ban, the first UN chief to visit Srebrenica since blue helmet peacekeepers failed to prevent the killing of around 8,000 Bosnian Muslims in 1995, said it was essential the international community learned the lessons of history.
"We have to do all to protect civilians and to stop bloodshed particularly in Syria now, when we have learned the message of Srebrenica," Ban said.
"The international community must be united not to see any further bloodshed in Syria because I do not want to see any of my successors after 20 years visiting Syria apologising for what we could have done now to protect the civilians in Syria which we are not doing."
Ban was speaking after meeting survivors at the Potocari cemetery near Srebrenica, where more than 6,500 victims of the genocide are buried.
The attacks took place after Bosnian Serbs brushed aside lightly armed Dutch peacekeepers in a so-called UN "safe area" where thousands of Muslims from surrounding villages had gathered for protection.
The episode caused huge damage to the reputation of the UN's peacekeeping operations, which were at the time headed by Kofi Annan -- Ban's predecessor and the man now tasked by the UN and Arab League to bring peace to Syria.
Annan's peace plan has struggled to make any headway, and half of a UN observer mission sent to supervise an April truce that never took hold was pulled out of Syria on Wednesday.
Asked if the UN -- which has failed to agree any sanctions over the Syrian conflict -- was ready for military intervention, he said: "What is important at this time that the violence must stop on both sides, government forces and opposition forces.
"Nobody is now talking, as I understand, (about) military operations," he Ban said before leaving Bosnia for London to attend the opening of the Olympic Games.
In Srebrenica, Ban acknowledged that the United Nations had let the people there down, calling it perhaps the most difficult and the most painful place for him to visit as secretary-general.
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"The international community failed to provide the necessary protection to many people who were killed at the time, when they needed our support," he said.
"Srebrenica is holy ground for the families and the victims and also for the Family of Nations."
Ban's visit received a mixed reaction from locals.
While some victims praised it, saying they hoped it will keep the United Nations from looking on if another genocide is carried out in the future, others dismissed it as too little, too late.
"There will be no justice as long as... the UN hides behind its immunity," Hajra Catic, who lost her husband and son in the slaughter, told journalists.
"The people who delivered my family to the (Bosnian) Serb forces were (UN) blue helmets," said Hasan Nuhanovic, a former interpreter for the Dutch UN battalion in Srebrenica who lost both parents and his brother in the massacre.
He added that Ban's visit was important "because the UN must take a position... (and) recognise its responsibility" for Srebrenica.
Nuhanovic is one of the plaintiffs in a lawsuit trying to hold the Dutch state responsible for the deaths of three Srebrenica victims including his father and brother.
In 2011, an appeals court found the Dutch state responsible, the first time it was held accountable by a judge for the actions of its UN peacekeeping battalion.
But the Dutch government announced last month it would appeal the ruling.
The Srebrenica massacre has been ruled a genocide by two international courts.
Two men accused of masterminding the slaughter, former Bosnian Serb political leader Radovan Karadzic and his army chief Ratko Mladic, are on trial at the UN's Yugoslav war crimes tribunal in The Hague after years on the run.