The UN Security Council in March 2005 had asked the ICC to launch an investigation into the violence in Darfur, which the United States has called genocide, a charge Khartoum denies.
"We eagerly await the prosecutor's recommendations for holding those responsible for the gravest crimes fully accountable," said Sudanese human rights lawyer Osman Hummaida.
Experts say some 200,000 people have been killed and 2.5 million others driven from their homes in Darfur since 2003, when rebels took up arms against the government, charging it with neglect. Khartoum says about 9,000 people have died.
"I hope the message that goes out from this action is that the days of absolute impunity that have existed for horrific crimes committed in Darfur are coming to an end," said Richard Dicker of New York-based Human Rights Watch.
UN and African Union observers blame pro-government militias, known as Janjawid, for the worst atrocities.
Mohamed Ali al-Mardi, Sudan's justice minister, was quoted as saying on Monday that the ICC had no jurisdiction over its nationals and it would not allow anybody, including rebels, to be tried outside Sudan.
Sudanese media also reported Khartoum would put several people on trial next week, including military personnel and paramilitary troops, for suspected involvement in attacks in Darfur.
Moreno-Ocampo has said he would examine whether Sudan's government is conducting its own judicial proceedings over Darfur as the ICC is only supposed to prosecute when national courts are unwilling or unable to act.
Rights groups say Khartoum's own investigations and tribunals for crimes in Darfur have been largely for show.
The ICC, the world's first permanent war crimes court, started work in 2002 and is now supported by 104 nations, although still not by Russia, China and the United States.
Washington fiercely opposed the creation of the ICC, fearing it would be used for politically motivated prosecutions of its citizens.
But Washington has refrained from blocking Darfur's referral to the ICC.