The International Criminal Court says it has credible information about grave crimes committed in Darfur, Sudan.
Millions of people have been displaced by the conflict
Prosecutor Luis Moreno Ocampo told the UN there were cases the court could take up, because of the inactivity of the Sudanese authorities.
The ICC can try those suspected of crimes against humanity when local courts are unable or unwilling to.
More than two million people have been forced from their homes in a conflict in which at least 180,000 have died.
Rape and destruction
The ICC's prosecutor told Security Council members there was a significant amount of evidence about the killing of thousands of civilians, widespread rape and destruction in Darfur.
Mr Moreno Ocampo said although the Sudanese government had set up various courts to try crimes in Darfur, they did not relate to the most serious cases, which he would focus on.
Darfur became the first case referred by the Security Council to the International Criminal Court.
An investigation by a UN-appointed commission drew up a list of suspects, but Mr Moreno Ocampo said he would decide who should be prosecuted.
And he stressed they were still monitoring events in Darfur.
"We are also vigilant to the ongoing commission of serious crimes in Darfur. The commencement of investigations marks an opportunity for parties to take all possible steps to prevent the continuation of such offences."
It is not clear how much co-operation Sudan will give the court.
Sudan's ambassador to the UN, Elfatih Mohammed Erwa, did not confirm reports that his government would refuse to hand over suspects to the court, and would only say they had not yet been asked.
There is no indication as to when Mr Ocampo will visit Sudan to see conditions in Darfur for himself.