Updated

U.N. Secretary General Ban Ki-moon paid his respects Thursday to the 8,000 victims of the 1995 Srebrenica massacre and said he does not want his successor to have to do the same 20 years from now in Syria.

Srebrenica was the worst massacre in Europe since World War II and took place in an area that was officially under U.N. protection during the 1992-95 Bosnian war. The U.N. has acknowledged its failure to protect the men and boys, who were killed by Serb forces.

"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 in 20 years visiting Syria and apologizing for what we could have done to protect the civilians which we are not doing now," he told reporters during a visit to a memorial-cemetery complex near Srebrenica.

He called on all sides in Syria to "stop fighting and killing people now" and urged the world to unite and act.

But he did not say exactly what should be done beyond keeping up pressure for Syrian President Bashar Assad to step down. He also did not criticize Russia and China by name for vetoing a Western-backed U.N. resolution threatening Assad's regime with sanctions.

The U.N. deployed a 300-member observer force to Syria to monitor a cease-fire as part of international envoy Kofi Annan's peace plan. But the cease-fire never took hold, and half of the observer mission has left the country amid mounting violence while those still in the country are largely confined to their hotels.

Ban placed white flowers at a low-lying circular granite wall engraved with victims' names, and called Srebrenica a "tragedy of epic proportions."