Family members laid to rest the remains of 534 victims, removed recently from mass graves, next to the existing 3,297 graves at the Srebrenica-Potocari memorial center.

Visitors and dignitaries prayed for the 8,100 Muslim men and boys who were killed in Srebrenica over several days in 1995 when Serbian forces overran the town.

U.S. Ambassador to Bosnia Charles English said that President Obama has called the Srebrenica slaughter "a stain in our collective consciousness," and that the world had to ask itself how this genocide could have happened.

During the 1992-95 Bosnian War, the United Nations declared Srebrenica - which had been besieged by Serbian forces throughout the war - a U.N.-protected safe area for civilians. A number of Bosnians flocked there for protection.

But in July 1995, Serbian troops led by Gen. Ratko Mladic overran the enclave. The outnumbered U.N. troops never fired a shot. They watched as Mladic's troops rounded up the population of Srebrenica and took the men away for execution.

It has been described by former Secretary-General Kofi Annan as the darkest page in U.N. history.

Every year, more victims' bodies are recovered from mass graves found in the area, identified through DNA analysis, and buried. This year, among the 534 victims, there are 44 teenagers. Four were 14 when they were killed.

Kadrija Muminagic arrived from Germany to bury his nephew Saidin, who was 14 when he and his father ended up at the execution field. Saidin's 16-year-old brother, Sulejman, was killed by a shell that landed close to their home a week before Srebrenica fell. Only the mother survived the massacre. She died three years later.

"She died of sorrow," said Muminagic, who escaped the killing by hiding in the forest.

The International Court of Justice in the Hague, Netherlands, has ruled that the Srebrenica massacre was genocide.

Former Serbian political leader Radovan Karadzic, is on trial at the U.N. war-crimes tribunal in the Hague. He claims he is not guilty of what happened. Mladic, also indicted on genocide charges, is still in hiding, apparently in Serbia. Belgrade has faced immense international pressure to arrest him.

In Serbia, President Boris Tadic said that the main obligation to the victims is to punish those responsible and that Serbia is doing all it can to track Mladic and send him to the Hague tribunal.

In 1995, about 15,000 men tried to escape the slaughter by fleeing over the mountains toward the safe town of Tuzla. They were hunted along their 65-mile walk; those caught were killed. At the time, Serbian TV filmed the hunt, and the footage was later used at the court as evidence. Many times it was aired on TV throughout the region. One section shows a man, Ramo Osmanovic, caught by Serbian soldiers and forced to call his 16-year-old son, Nermin, to come out from the forest and surrender. The boy obeyed.

Both have been found in mass graves and were being buried yesterday.

A U.S. congressional delegation was at the ceremony, led by Rep. Russ Carnahan (D., Mo.), who laid a wreath at the Memorial Stone.