Judges at the International Criminal Court have asked for more evidence before deciding whether to issue an arrest warrant against Sudan's leader.
Chief prosecutor Luis Moreno Ocampo wants the court to issue a warrant for President Omar al-Bashir over war crimes allegedly committed in Darfur.
Mr Ocampo has been given a month to provide the additional evidence.
President Bashir has denied the charges and Sudan has been lobbying to get the investigation delayed.
The African Union and Arab League agree with Sudan that any arrest warrant could jeopardise the peace process in Darfur.
The UN estimates that up to 2.7 million people have been forced from their homes and some 300,000 have died during the five-year conflict in Sudan's western Darfur region.
Sudan's government has always denied charges that it armed the Janjaweed militias accused of widespread atrocities against civilians in Darfur.
Mr Bashir launched a new initiative to bring peace to Darfur on Thursday, however the rebels and opposition parties did not take part.
One rebel spokesman said the move was an attempt to "circumvent" international justice.
Mr Moreno Ocampo asked the ICC to issue an arrest warrant against Mr Bashir in July, saying there were grounds to believe Sudan's president bore criminal responsibility on 10 counts of genocide, crimes against humanity and war crimes.
But a statement from the ICC on Thursday said that prosecutors must submit "additional supporting materials in relation to some confidential aspects" of the prosecution's request by 17 November.
Alex de Waal, an expert on the Darfur conflict based in the US, said it was very unlikely that it would affect the likelihood that the pre-trial chamber would issue an arrest warrant against Mr Bashir.
"What is not in much doubt is that the charges of war crimes and crimes against humanity will pass the rather low threshold... It's almost inconceivable that the pre-trial chamber would throw out those charges."
But he said the court may say there is insufficient evidence to bring "credible charges" of genocide against the Sudanese president.
Black African rebels took up arms in 2003, accusing Mr Bashir's Arab-dominated government of ignoring the region.
He blames the violence on the rebels and says the extent of the suffering has been exaggerated by the West for political reasons.