"Genocide is a crime against humanity as a whole, not just against it's immediate targets. It therefore falls on the world at large to act."
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On Saturday, Eliasson said: "I think the next month or two are going to be absolutely crucial for the future of Darfur."
The AU said Salim has extracted a commitment from Khalil Ibrahim, justice and equality movement (JEM) group chief, "to take part in all future negotiations aimed at completing the process of creating a final and lasting peace in Darfur".
Khartoum, which has been accused of sponsoring a genocidal crackdown on the fighting groups through its Janajaweed militia, has assured the UN that it does not seek a military solution to the four-year conflict.
Ali Al-Sadiq, the Sudanese foreign ministry spokesman, said: "The Darfur dispute should be resolved through peaceful negotiation only."
The UN estimates some 200,000 people have been killed in Darfur and two million displaced from the region.
A May 2006 peace deal failed to halt the fighting.
UN and AU negotiators are in near daily contact with the rebel groups, numbering around a dozen, but many have not yet agreed to join the talks, Eliasson said.
Ali Triki, who heads the Africa desk at the Libyan foreign ministry, said that "representatives of most of the Sudanese rebel movements are also in Tripoli for talks on the sidelines of the conference.
"The meeting will fix a date for the start of negotiations with the rebel groups that did not sign the Abuja accord" last year, he said.
Five rebel factions formed a new alliance on Saturday in Asmara to present a united front for peace negotiations with Khartoum and appealed "to all other movements to unify efforts," they said in a statement.
But several major rebel groups, including the Sudan Liberation Movement, the Greater Sudan Liberation Movement and the JEM, remain outside the new alliance.
Many competing initiatives have been presented by neighbouring countries, including Egypt, Eritrea and Libya which could be synthesised into a single coherent approach in Tripoli, Eliasson said.
Also attending are the UK, Canada, Chad, China, France, the Netherlands, Norway, Russia, the US, the Arab League and the European Union as well as Sudan.