Appeal judges at the tribunal reversed a decision that prosecutors had not provided enough evidence to add genocide to al- Bashir's charge sheet, ruling that the ICC's pretrial chamber must look again at whether he should face the charge.
The Sudanese leader has already been charged on seven counts of crimes against humanity and war crimes, including murder, extermination, torture and rape.
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, appeal judge Erkki Kourula of Finland said yesterday.
The ruling puts other leaders on notice that the court will not balk at charging them with genocide if they persecute their own people. It may also mean the court ignored the AU plea for al-Bashir's warrant to be suspended to give peace efforts in Darfur a chance.
Former president Thabo Mbeki made the representation to the ICC via the United Nations Security Council in 2008.
Mbeki leads a high-level panel on Darfur. His spokesman, Mukoni Ratshitanga, said yesterday Mbeki would not comment as the ruling had "no bearing" on the mandate of the panel.
However, Mbeki told reporters in Addis Ababa last July his panel was working within the AU position calling for the indictment of al-Bashir to be deferred and for there to be a delay in the serving of warrants against him.
The arrest warrant against al-Bashir was the first to be issued against a sitting head of state by the ICC.
However, the ICC has no police force, and relies on national authorities and states signed up to the court to make arrests. It does not hold trials in absentia, so al-Bashir cannot be tried or convicted until his arrest.
In its ruling yesterday, the appeals chamber said the pretrial chamber had set too high a threshold for evidence needed to include genocide in the arrest warrant.
A ruling on whether to add genocide to the list of charges would not take place quickly, but could take a few months.
Activists welcomed yesterday's ground-breaking decision, which helps define just how much evidence prosecutors need before judges at the world's first permanent war crimes tribunal 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 nongovernment group that supports the court.
The five-judge appeals chamber said the ICC had concluded wrongly last March that there was insufficient evidence to charge al-Bashir on 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 refuses to recognise the court's jurisdiction, and has vowed never to surrender.
Rabie Abdel-Attie, a Sudanese government spokesman, said that the court's decision reflected its increasing isolation from reality on the ground in Sudan.
He said the decision would not affect al-Bashir's bid to run again as a presidential candidate at elections expected in April.
"The government doesn't give the court any consideration, and doesn't care much for it." With Sapa-AFP-AP, Reuters