The government of Sudan and a southern rebel group have formally launched the final phase of their peace negotiations to end a 21-year war that has claimed two million lives.

Negotiators say they are optimistic the final details on a permanent cease-fire in southern Sudan can be worked out in the coming weeks.

On Saturday, they signed an agreement pledging to wrap up their talks in the shortest time possible, once the negotiations resume in Kenya on June 22. Mediators hope the final accord can be finished by mid-July.

The two sides reached a landmark agreement last month on dividing political power, and an earlier accord set the terms for sharing Sudan's oil wealth.

The chief of the rebel Sudan People's Liberation Army, John Garang, says the peace deal will change his country forever.

"Sudan cannot and will never be the same again, as this peace agreement will engulf the country in democratic and fundamental transformation, instead of being engulfed in war, as it has been since independence," he said.

The Sudanese vice president, Ali Osman Taha said all the people of Sudan have a stake in the peace accord.

"This agreement will be owned by all of them, and with this we declare that we have entered a new era, where we and the international community and the whole region and our brothers will be all together helping us," the vice president said.

The Kenya talks include only the Muslim Arab-controlled government and the southern rebels, who are black Africans practicing Christianity or traditional religions.

But another major civil war is raging in western Sudan's Darfur region, where Arab militiamen, backed by the government, are fighting rebels, who are also Muslims, but of black African origin. Relief agencies say one million blacks have been driven from their homes in what is described as a campaign of ethnic cleansing.

Norway's observer at the Sudan peace talks, International Development Minister Hilde Johnson, referred to the Darfur crisis at Saturday's ceremony.

"The world community now expects that this final negotiation period is also used in parallel to settle the conflict in Darfur," said Hilde Johnson. "We will urge the parties to a common commitment to this end."

U.N. Secretary-General Kofi Annan sent a message to the gathering, saying the Darfur conflict, "continues to cause appalling suffering that demands a concerted international response."

Kenya's president, Mwai Kibaki, said Sudan's peace process should set an example for the rest of Africa.

"I hope that the success of the Sudan peace process will serve as a catalyst for the peaceful resolution of other conflicts in Africa," he said. "It is important that we in Africa develop a culture of tolerance and peaceful coexistence."

President Kibaki invited the parties to sign the final peace agreement in Nairobi, once their negotiations are concluded.