The world's first permanent war crimes court has sworn in its first 18 judges in a move hailed as the biggest legal milestone since the Nuremberg trials.
The International Criminal Court's (ICC) judges - 11 men and seven women - will try charges of genocide, crimes against humanity and war crimes at the court in the Dutch capital of The Hague.
Eighty-nine countries have backed the court to try alleged crimes committed from when it came into being in July 2002. But the United States, China and Russia have refused to recognise the court.
The ICC has been given added impetus by ad hoc UN war crimes tribunals set up to try war crimes in the Balkans in the 1990s and the 1994 Rwandan genocide.
"The court which we have created, and in which we install judges today, responds to one of the darkest parts of our human experience, and yet this is also a ceremony of hope," said Jordan's Prince Zeid Ra'ad Zeid Al-Hussein, head of the assembly of states who backed the Rome Statute in 1998 to set up the ICC.
The United States has actively campaigned against the setting up of the court fearing troops could face politically motivated prosecutions. Washington today declined an invitation to join UN Secretary-General Mr Kofi Annan and hundreds of other guests at the inaugural session.
The United States, which has withdrawn its signature from the 1998 treaty that set up the ICC, has been persuading other countries to seal bilateral agreements exempting all US citizens from the court's authority. Supporters of the court said the row would not remove the symbolism of the inauguration, hosted by Dutch head of state Queen Beatrix.
Anyone - from a head of state to an ordinary citizen - will be liable to ICC prosecution for human rights violations, including systematic murder, torture, rape and sexual slavery.
The court officially opened in The Hague last year after 60 states backed it, but with just a skeleton administrative staff it had no prosecutor or judges to make it truly operational.
The ICC's first judges were elected in New York earlier this year but a prosecutor still has to be appointed.
Since it was officially set up last July, the ICC has received more than 200 complaints alleging war crimes. When appointed, the prosecutor will decide on how to proceed.
The new tribunal has jurisdiction only when countries are unwilling or unable to prosecute individuals for atrocities. Cases can be referred by states that have ratified the treaty, the UN Security Council or the tribunal's prosecutor after approval from three judges.
The court is not retroactive and will not probe crimes committed before July 1st, 2002.
Unlike the U.N. war crimes tribunals for Yugoslavia and Rwanda - based in The Hague and Arusha in Tanzania - the ICC is not a United Nations body.