The International Criminal Court has announced an inquiry into alleged war crimes in west Sudan's Darfur region.
Some two million people have fled their homes in Darfur, the UN says
The Hague court's chief prosecutor, Luis Moreno Ocampo, said on Monday it was launching what will be the ICC's biggest investigation.
The BBC's Martin Lumb says this is the first time the court has used its right to pursue a case where a host state is thought unwilling or unable to do so.
A special UN inquiry has given the ICC the names of 51 potential suspects.
The UN says about 180,000 people have died in the two-year Darfur conflict.
It says more than two million people have been forced to leave their homes in the region.
The announcement by Mr Ocampo comes two months after the situation in Darfur was referred to the ICC following a vote at the UN Security Council - the first time the council has referred a case to the ICC.
The ICC statement said the investigation would be based on thousands of documents received by the court and interviews with more than 50 independent experts.
INTERNATIONAL CRIMINAL COURT
First permanent court to try individuals for genocide, war crimes and other human rights violations
Rome Statute set up in July 1998, when 120 countries adopted the treaty
Came into force in April 2002 after ratification by 60 countries
Uganda and DR Congo investigations began in 2004
"The investigation will require sustained co-operation from national and international authorities," Mr Ocampo said in the statement.
"It will form part of a collective effort, complementing African Union and other initiatives to end the violence in Darfur and to promote justice.
"Traditional African mechanisms can be an important tool to complement these efforts and achieve local reconciliation."
Our correspondent says that by launching the investigation now the court has rejected more cautious advice that the case should wait until the conflict is completely resolved.
Other trials will be held later this year against alleged perpetrators of war crimes in two other African nations, Uganda and Congo.
However, in these cases the governments themselves turned to The Hague for justice.
The Sudanese ambassador in the UK, Hassan Abdin, told the BBC his government would stick to a decision taken immediately after the Security Council resolution not to hand over its citizens for trial abroad.
But he said Khartoum was willing to discuss with ICC prosecutors requests to try suspects inside the country.
US backed down
The Security Council cited allegations of rape, murder and plunder in Darfur.
The New York-based Human Rights Watch group said the Sudanese authorities in Khartoum have not taken any meaningful steps to bring to account those responsible for the alleged crimes.
The referral to the court was made possible when the US - which opposes the ICC - backed away from using its veto power as the Council's permanent member.
The US has expressed its concerns that the court could bring bogus charges against American nationals.
Washington has already signed nearly 100 bilateral treaties with countries that have agreed not to surrender US citizens to the ICC.
However, 99 countries have ratified the court's founding treaty, including all of Washington's major allies in Europe.
Send us your comments on the form below
It is excellent that we have a new international body which can call foul when an oppressive regime like Sudan's crosses the line on human rights and refuses to leave the "wrong side". If the Security Council and selfish industrialized nations will not respond appropriately (to my mind, deploying peacekeeping troops) to the Darfur crisis, then at least the ICC can do so.
Emile Scheffel, Kamloops, Canada
This is an important step toward ending the Darfur crisis and providing justice for the millions affected by it. When the Security Council passed this resolution I was thrilled, despite the misgivings of the United States. The United States should not be so concerned about its own citizens facing charges from the ICC. This only makes us look cowardly and as if we have something to hide. There could very well be good reason to try American citizens for war crimes associated with the War on Terror. By refusing to let our citizens be tried by the ICC we come across in the same way that Sudan does when it refuses to let its citizens be tried by the ICC.
Jackson Smith, Boise, ID, USA
Why did innocent people have die in Sudan, even those who did not have anything to do with the war in Sudan and even those in Liberia? During the last seven years, thousands of people have died and yet there is no solution for their problems.
Gabriel Quarty, Garland- USA
The Court's investigation opens a new era in international relations where rule of law is finally enforced by a global Court system. For human rights civil society in Southeast Asia, the impact will be significant.
Niza Concepcion , Bangkok Thailand
While thousands suffer and die, the world's powers "fiddle". Get on with it! Save the Black Africans of Darfur and the Southern Sudan now! Enough talk.
Bonita Angelini-Caracciolo, Charleston, SC USA
Human rights and state sovereignty have been in conflict for many years. But now in Darfur there seems to be wide acceptance that Sudan's government has lost much of its legitimacy because of their human rights violations. The question we must ask is how universal will the international community apply this new relationship between sovereignty and human rights? Sudan is a weak state, but what of a strong state, like China, North Korea, Iran, or even according to Amnesty International the United States? Will the ICC treat them the same way?
Nick Roscoe, Boston, USA
Sudan GOS will not in anyway accept or handover the suspects even one metre from the border instead they are only busy to see in to it that UN stops any trial or case. Their major thing is how to make Southerners fight themselves so that the peace ends and they will back any militia group on their side, which they are doing now.
Emmanuel A Solomon, Yei South Sudan
Why war crime charges are laid only of poor countries (exception was Germany)? There has never been a war crime trial by the ICC for crimes committed by Americans in wars of South East Asia and lately Afghanistan and Iraq.
Saim, Milton, Ontario, Canada
The BBC may edit your comments and not all emails will be published. Your comments may be published on any BBC media worldwide.