Appeal judges at The International Criminal Court in The Hague today overturned a ruling that Sudan's leader cannot be charged with genocide in Darfur.
The unprecedented decision could lead to President Omar al-Bashir's indictment with humanity's worst crime.
The appeals ruling also put other leaders around the world on notice that the court will not balk at charging them with genocide if they persecute their own people.
The standard of proof the court used last year to dismiss three counts of genocide against al-Bashir "was higher and more demanding than what is required" in its statutes, appellate judge Erkki Kourula of Finland said.
Activists welcomed the groundbreaking decision, which helps define just how much evidence prosecutors need before judges at the world's first permanent war crimes tribunal will issue an indictment.
"Today's ruling is hugely significant, as it could lead to the inclusion of charges of genocide by ICC judges for a sitting head of state and for the first time in the history of the court," said William R Pace of the Coalition for the ICC, a non-government group that supports the court.
The five-judge appeals chamber said the International Criminal Court wrongly concluded in March that there was insufficient evidence to charge al-Bashir with three counts of genocide for allegedly attempting to wipe out entire ethnic groups in the war-ravaged province of Darfur.
Instead, the court charged him with seven counts of war crimes and crimes against humanity for allegedly orchestrating a campaign of murder, torture, rape and forced expulsions in Darfur.
Al-Bashir, the first sitting head of state indicted by the world's first permanent war crimes tribunal, refuses to recognise the court's jurisdiction and has vowed never to surrender.
Rabie Abdel-Attie, a Sudan government spokesman, said the decision will not affect al-Bashir's bid to run again for presidency at elections expected in April.
"The government doesn't give the court any consideration and doesn't care much for it. This is a matter of principle," he told The Associated Press from Khartoum.
"The court is heading in one direction, and we in the other."
Al-Bashir's indictment in March further isolated his hardline regime. Since the charges were issued, the Sudanese leader has travelled to friendly countries but called off trips to nations where he fears he could be arrested and sent to The Hague.
His government expelled 13 international aid agencies working in Darfur in response to the charges, further compounding the humanitarian crisis in a region where 300,000 people have died since fighting broke out in 2003 between the government and rebels. The United Nations says 2.7 million people have been driven from their homes.
Prosecutor Luis Moreno Ocampo said the decision to expel aid agencies bolsters his genocide case against al-Bashir.
"For me, the fact that President Bashir expelled the humanitarian organisations is confirming that his intention is the physical destruction of these people," he told reporters.
He accused al-Bashir of keeping 2.5 million refugees "under genocide conditions, like a gigantic Auschwitz".
Moreno Ocampo accuses al-Bashir of mobilising the entire Sudanese state apparatus with the aim of destroying a substantial part of the Fur, Masalit and Zaghawa ethnic groups in Darfur over more than six years.
Prosecutors accuse Sudanese troops and the janjaweed Arab militia they support of murdering civilians and preying on them in refugee camps. Moreno Ocampo said part of the alleged genocide was a campaign of rape to drive women into the desert, where they die of starvation.
Analysts said March's decision was vital in laying the groundwork for potential indictments of other leaders who have been mentioned as possible targets of war crimes investigations as it rejected head of state immunity protections.