(Adds details on agreement, quotes)

By Omar Hassan

DJIBOUTI, June 9 (Reuters) - Somalia's interim government signed a peace deal on Monday with some opposition figures at U.N.-led talks in Djibouti that had looked on the brink of failure, a U.N. official said.

Hopes had dimmed after both delegations refused for days to meet face-to-face to discuss ways of ending 18 years of conflict that have wracked the Horn of Africa nation.

"We have a peace deal," an aide to the U.N. envoy for Somalia, Ahmedou Ould-Abdallah, told Reuters by telephone.

"They agreed on the termination of all acts of armed confrontation … to come into force 30 days from the signing of the agreement for an initial period of 90 days, renewable."

The aide said the agreement also called for the United Nations to authorize deployment of an international stabilization force.

Within 120 days, Ethiopian forces helping the government fight Islamist-led insurgents would then leave, the aide said, conditional on the deployment of sufficient U.N. troops.

Hardline members of Somalia's opposition had rubbished other opposition figures who took part in the meetings, casting doubt on the implementation of any deal. Insurgent leaders inside Somalia also denounced the talks.

A contingent of 2,200 African peacekeepers has made little headway stemming the conflict, and the United Nations is reluctant to intervene until security improves.

Late on Sunday, Ould-Abdallah said delegates had separately agreed on some issues like humanitarian aid, but that he had decided to halt the discussions, with the main sticking point being the presence of Ethiopian forces.

He had persuaded teams from both sides to come twice to neighbouring Djibouti in May and this month. But they declined to meet directly -- until Monday's signing ceremony.

Fighting between Islamist guerrillas and Somali-Ethiopian troops killed at least 28 people over the weekend in Mogadishu.

The rebels are waging an Iraq-style insurgency of roadside bombings, ambushes and assassinations.

The violence has triggered a humanitarian crisis that aid workers say may be the worst in Africa, with at least a million refugees in a nation torn by constant civil conflict since the 1991 toppling of a military dictator by warlords. (Additional reporting and writing by Daniel Wallis in Nairobi; Editing by Stephen Weeks) (For full Reuters Africa coverage and to have your say on the top issues, visit: http://africa.reuters.com/)

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