Bosnia is ready to act in case migrants change course, its foreign minister said Monday, reflecting wider concerns about EU moves to close the current route through other Balkan states.

Speaking on a visit to Cyprus, Igor Crnadak appealed for a "united response by Europe" to the worst refugee crisis to hit the continent since World War II.

The Bosnian government called Monday for a probe to track down those behind an attack on Serbia's premier during commemorations marking the 20th anniversary of the Srebrenica massacre.

Prime Minister Aleksander Vucic was chased from the Srebrenica memorial site on Saturday by a mob hurling bottles and stones in an assault that laid bare the wounds that still run deep after the Balkans conflicts of the 1990s.

Serbian Prime Minister Aleksandar Vucic on Saturday affirmed his commitment to reconciliation with Bosnian Muslims after a stone-throwing mob chased him from a ceremony marking the 20th anniversary of the Srebrenica massacre.

"I regret that something like this has happened. I regret that some did not recognize our sincere intention to build a sincere friendship between Serbs and Bosniaks (Muslims)," Vucic told reporters upon his return to Belgrade. "My hand remains outstretched (to Bosnian Muslims) and I will continue with my policy of reconciliation" between the two Balkan nations, he said.

Bosnia commemorates Saturday the 20th anniversary of the massacre of some 8,000 Muslim men and boys in the U.N.-protected enclave of Srebrenica, as debate continues to rage over its description as genocide.

The remains of 136 newly-identified victims will be laid to rest along with more than 6,000 others already buried at a memorial center just outside the eastern Bosnian town.

As the top Bosnian Serb leaders of the time, Radovan Karadzic and Ratko Mladic are the alleged chief architects of the Srebrenica massacre. But, 20 years on, they have yet to be sentenced for Europe's worst atrocity since World War II.

Karadzic, the Serbs' political leader during Bosnia's brutal 1992-1995 civil war, and his military chief Mladic were both on the run for years before their separate arrests.

Survivors of the Srebrenica massacre set out with thousands of others Wednesday on a solemn 105-kilometer march ahead of the 20th anniversary of the killing of nearly 8,000 Muslims near the U.N.-protected enclave.

Their route across Bosnia retraces the one taken by the men and boys fleeing Bosnian Serb forces who later overran Srebrenica, setting the stage for what many describe as a genocide.

The U.N. Security Council was headed for a showdown Tuesday over a draft resolution that would formally recognize the Srebrenica massacre as genocide, after Russia threatened to use its veto.

As Bosnia prepares for somber national commemorations of the 20th anniversary on Saturday, the 15-member council was to vote on a text that condemns the killing of some 8,000 Muslim men and boys by Bosnian Serb forces in July 1995.

The United States extradited Thursday to Bosnia a former Muslim prison guard accused to have abused Serb civilian detainees during the 1992-1995 war, prosecutor's office said.

Almaz Nezirovic, one of rare Muslims to be indicted by Bosnia's prosecutors for war crimes, is suspected to have participated in "torture" of Serbs in a detention camp in the northern Bosnian region of Derventa between April and July 1992.

A former Bosnian Serb soldier was acquitted Thursday of charges he helped kill hundreds of Muslims during the Srebrenica genocide, just about a week before commemorations of the massacre's 20th anniversary.

Aleksandar Cvetkovic was tried by a Bosnian court.

The ethnic Serb chairman of Bosnia's rotating presidency on Monday urged the U.N. to not adopt a resolution on the Srebrenica genocide, saying it would destabilize the country already split along ethnic lines.

"I must warn you that the current (inter-ethnic) situation is bad and call on you to recognize that the adoption of this resolution would not be a good thing for the stability of Bosnia," Mladen Ivanic wrote in a letter to U.N. Secretary General Ban Ki-moon.