Appeals judges at the United Nations' Yugoslav war crimes tribunal in The Netherlands have reinstated a genocide charge against Radovan Karadzic linked to a campaign of killing and mistreating non-Serbs at the start of the Bosnian war in 1992.
The decision on Thursday reversed the former Bosnian Serb leader's acquittal last year on one of the two genocide charges he faces.
Appeals judges said the trial chamber "erred in fact in concluding that there was no evidence" of genocidal intent in relation to the killings allegedly carried out by Bosnian Serbs of Muslims and Croats in Bosnian municipalities from March to December 1992.
"The appeals chamber... reverses the trial chamber's acquittal of Mr Karadzic for genocide... and reinstates the charges," Judge Theodor Meron told the International Criminal Tribunal for the former Yugoslavia (ICTY).
Thursday's ruling is likely to further draw out his long-running trial on 10 other charges including another genocide count for allegedly masterminding the 1995 Srebrenica genocide.
Karadzic, 68, now faces 11 charges, including two counts of genocide as well as accusations of war crimes and crimes against humanity.
He denies the allegations against him, all of which relate to his role in the Balkan country's 1992-95 inter-ethnic war, in which 100,000 people were killed and about 2.2 million others became homeless.
The first genocide charge relates to a campaign to "permanently remove" Bosnian Croats and Muslims from towns and cities, collectively referred to as Bosnia's "municipalities", and claim the land as Bosnian Serb territory.
A second genocide charge covers the 1995 genocide at eastern Bosnia's Srebrenica, where about 8,000 Muslim men and boys were slaughtered and buried in mass graves.
Judges last year dropped the first genocide charge saying there was no evidence to convict Karadzic for genocide in the municipalities.
But appeals judges on Thursday said the decision "resulted in a miscarriage of justice".
They said there was evidence from meetings attended by Karadzic in the early 1990s "that it had been decided that one third Muslims would be killed, one third would be converted to the Orthodox religion and a third will leave on their own".
Judge Meron added that based on evidence during Karadzic's trial - including reports of rape and violent beatings of Bosnian Muslims and Croat detainees having their "heads hit against walls" - "no reasonable trial chamber" could have concluded that the evidence was insufficient.
Genocide is the gravest crime under international humanitarian law - and the hardest to prove.
Karadzic is also being prosecuted at the UN court for his role in the 44-month siege of the Bosnian capital Sarajevo between May 1992 and November 1995 in which 10,000 people died.
He faces charges for his part in taking hostage UN observers and peacekeepers and using them as human shields during a NATO bombing campaign against Bosnian Serb military targets.
Arrested on a Belgrade bus in 2008 after years on the run, the carefully quaffed Karadzic was wanted in particular for masterminding the Srebrenica killings.
Thursday marked the 18th anniversary of the Srebrenica genocide, deemed Europe's worst wartime atrocity since World War II.
At Srebrenica on Thursday, 409 war victims, including a newborn baby, were reburied in a sombre funeral service after their remains were identified nearly two decades after they were dumped in mass graves.