A crowd throwing bottles and stones has chased Serbia's prime minister from a ceremony in Bosnia marking the 20th anniversary of the Srebrenica massacre, underscoring the depth of anger over Belgrade's continued denial of the crime as genocide.

Aleksandar Vucic had just laid flowers at a monument for thousands of victims identified and buried there when the crowd started to chant "Allahu Akbar" (God is Great) while hurling objects at the prime minister.

Bodyguards whisked Mr Vucic through angry mourners shouting and booing, while a crowd surged up the hill behind the delegation as they ran for their cars.

Serbia's Tanjug state-run news agency said the prime minister was hit on the head by a stone and had his glasses broken.

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Serbia's interior minister Nebojsa Stefanovic described the attack as an "assassination attempt".

"This is a scandalous attack and I can say it can be seen as an assassination attempt," Mr Stefanovic said on Serbian Pink television.

"Bosnia has failed to create even the minimal conditions for the safety of the prime minister."

The scene marred a ceremony to commemorate the day that Srebrenica, designated a safe haven protected by Dutch United Nations peacekeepers, fell to Bosnian Serb forces in the closing months of the 1992 to 1995 war.

Tens of thousands turned out to pay their respects, as 136 more coffins of identified victims were brought to the memorial centre to be buried the next day.

Bosnian soldiers in battlefield uniforms, survivors of the massacre, and ordinary people carried the coffins, wrapped in green, several hundred metres from a hangar that served as a UN base 20 years ago to the Srebrenica memorial cemetery.

Women silently cried as the coffins were laid out on a lawn before being buried during the ceremony.

Among the 136 victims, identified last year by DNA tests, were members of families that lost all of their male members in the killing, according to the Bosnian institute for missing persons.

To date, 6,241 victims have been found, identified and buried at the memorial centre.

About 230 others have been laid to rest in other cemeteries at their families' request.

Some 8,000 Muslim men and boys were killed by Bosnian Serb forces at Srebrenica, then a UN-protected Muslim enclave, in the worst atrocity in Europe since World War II.

The massacre has been qualified as genocide by two international courts.

The remains of victims to be buried on July 11 (local time) had been found in several mass graves or in forests where men were killed in ambushes.

In most cases, only parts of the remains were found as their bones were moved from mass graves to so-called "secondary" graves in an effort to hide the true extent of the massacre.

An elderly Bosnian woman walks past the coffins of 136 newly identified victims of the 1995 Srebrenica massacre. ( AFP: Dimitar Dilkoff )

Russia backflips on 'genocide' UN solution

On Wednesday, Russia — backed by ally Serbia — vetoed a United Nations Security Council resolution that would have condemned the massacre as a genocide.

Russia's ambassador to the UN, Vitaly Churkin, said the British-drafted resolution to call the massacre "a crime of genocide" unfairly singled out Bosnian Serbs for war crimes.

But days after it vetoed the resolution, Russia's foreign ministry called for all people responsible to be brought to justice.

"We strongly advocate that all persons who participated in these and other crimes in Bosnia and Herzegovina should face justice and be punished as soon as possible," it said in statement.

Many Serbs dispute the term genocide, the death toll and the official account of what went on, reflecting conflicting narratives about the Yugoslav wars which still feed political divisions and stifle progress toward integration with western Europe.

During the 1990s, Mr Vucic was a disciple of the "Greater Serbia" ideology that fuelled much of the bloodshed accompanying Yugoslavia's demise.

He has since rebranded himself as pro-Western and his attendance on Saturday was intended to be symbolic of how far the region has come since wars that left at least 135,000 people dead - 100,000 of them in Bosnia.

"Look at him (Mr Vucic) and look at those thousands of tombstones," said Hamida Dzanovic, who had come to bury two bones identified by DNA as those of her missing husband.

"Is he not ashamed to say that this was not genocide? Is he not ashamed to come here?" she asked, recalling the last time she saw her husband.

"I remember him returning twice to kiss our children, like he knew we would never see each other again."

Reuters/AFP