ADDIS ABABA, Ethiopia — Secretary of State Rice urged some of Africa’s most unstable states yesterday to restore security and shore up faltering peace deals, but a Sudanese faction’s rebuff and the Somali president’s illness stole momentum from her attempts at diplomacy.

In a hectic series of meetings in the Ethiopian capital, Ms. Rice tried to calm the volatile Great Lakes region, ease rising tensions between Ethiopia and Eritrea and violence in Somalia, cool the conflict in Sudan’s Darfur province, and salvage a shaky north-south Sudan peace deal.

Ms. Rice had said she wanted to tackle elements of the Darfur conflict and bolster the 2005 peace deal that ended a separate, long-running north-south civil war. But the government of President al-Bashir of Sudan skipped the meeting, although Ms. Rice went on to meet southern Sudanese leaders, according to a list of delegates released by the American Embassy.

In Khartoum, Sudan, a ruling party official said the government, from which southern officials recently withdrew, had skipped the talks because it did not want Ms. Rice to intervene in the north-south dispute. He spoke on condition of anonymity because of the sensitivity of the issue.

The Sudanese government’s official explanation was that it had received invitations “only a few days ago,” not giving senior officials enough time to rearrange schedules.

“Our absence is not a sign of defiance,” Ali Sadiq, the spokesman for Sudan’s Foreign Ministry, said in Khartoum. “If they [the U.S.] had told us earlier, we would have come.”

Washington-Khartoum relations have been strained, with American leaders accusing the government of atrocities in Darfur and Khartoum bristling at Western pressure to allow international peacekeepers in Darfur. But Washington also sees Khartoum as an ally in the war on terrorism.

Earlier, Ms. Rice said she wanted to focus on overcoming logistical hurdles holding up a joint U.N.-African Union peacekeeping force for Darfur, a vast region ravaged by years of conflict.

More than 200,000 people have died and 2.5 million displaced since February 2003 when Darfur’s ethnic African rebels took up arms against the Arab-dominated central government, accusing it of neglect. As for the 2005 peace deal between Mr. Bashir’s government and southern rebels, she said “it’s time to refocus our efforts there.” “That is really an agreement that we cannot afford to let unravel,” Ms. Rice said.

Also yesterday, Ms. Rice urged more nations from the continent to send peacekeepers to war-battered Somalia — a country the United Nations says is facing Africa’s worst humanitarian crisis.

About 1,800 Ugandan peacekeepers are in Somalia, officially as the vanguard of a larger A.U. peacekeeping force, though no other countries have sent reinforcements so far.