Forensic experts have begun work to open what is believed to be the largest mass grave ever found in Bosnia.
The grave is thought to contain up to 700 bodies
Bulldozers removed a layer of topsoil to reveal human bones, as the area was marked off with tapes.
The grave is thought to contain the remains of up to 700 Muslim men and boys - many of them killed after the fall of the town of Srebrenica to Bosnian Serb forces in July 1995.
It could take more than a month to uncover all the bodies, officials said.
Information about the site, in an area known as Crni Vrh, or Black Peak, was provided by the United Nations war crimes tribunal in The Hague.
The UN was tipped off by someone who witnessed the burials, although it is not known whether the unnamed person took part in the actual task.
"We believe the grave contains several hundred bodies of 1995 Srebrenica massacre victims and those of Zvornik civilians killed at
the start of the war," said Murat Hurtic, a member of the Bosnian Muslim commission for missing people.
"It could be the largest mass grave ever found in Bosnia," he added.
It is still uncertain just how many people are buried in the grave - if it does indeed hold about 700 people it would be twice as large as any other mass grave found in Bosnia.
The four-by-20 metre (yard) grave was discovered two years ago.
Srebrenica: Regarded as the worst atrocity in Europe since World War II
The BBC's correspondent in Sarajevo, Nick Hawton, says it is surrounded by woodland and lies in mountainous territory, just a few kilometres from the border with Serbia.
The area used to be a front line and the ground is still strewn with mines.
The majority of the dead are thought to be victims of the Srebrenica massacre, when 7,000 Muslims were killed by Bosnian Serb forces, who were executed after Serb forces overran the UN-protected enclave.
The event is regarded as the worst atrocity on European soil since World War II.
The bodies were dumped in numerous graves across the region, and every year more of these sites are discovered.
Weeks of painstaking work lie ahead before forensic experts establish just how many people are buried and then begin the difficult task of identifying them.
The task may be complicated further by the fact that the bodies are thought to have been moved from an earlier grave by the Serbs and reburied to avoid detection.
The skeletons in such graves have often been crushed by bulldozers and body parts get mixed together.
Experts may have to turn to DNA analysis for identification - a long and expensive process.
But our correspondent says this is just the tip of an iceberg - there are still around 20,000 people missing from the Bosnian war.
The head of the Bosnian Commission for Missing Persons, Amor Masovic, says the discovery of every new grave helps relatives finally come to terms with what happened to their loved ones.