The president of Ivory Coast installed an opposition leader as prime minister today, accepting the first part of a French-brokered plan to end months of violence in this once stable West African country. But rebel leaders threatened a return to civil war by Friday unless there are further moves toward implementing a coalition government.

"This is the price of peace in the country," said President Laurent Gbagbo, surrounded by other African leaders and foreign diplomats as he spoke here at a festive ceremony. "We need time to convince as well as be convinced. This will allow us to start a new era in the history of the Ivory Coast."

President John Kufuor of Ghana escorted the opposition leader, Seydou Diarra, to the Ivorian capital from Accra, Ghana, and officiated at the swearing-in. Leaders from nearby Nigeria and Togo accompanied Kufuor and Diarra, a Muslim from Ivory Coast's rebel-controlled north. "This is an important step for all sides," Kufuor said. "We are assured that all sides will use this as a guide."

Also on hand were diplomats from France, South Africa and the United Nations, who hope to ensure Gbagbo's compliance with terms of the peace accord, signed in France last month.

Diarra, who also served as prime minister during a coalition government in 2000, had attended the French talks. "With the help of the head of state, I am here to help bring peace to Ivory Coast," he said in a brief arrival statement.

Representatives of the northern-based insurgency were conspicuously absent and were threatening a return to war unless there was full implementation of the Jan. 24 peace accord, which was signed by Gbagbo and rebel leaders. The accord, intended as a general framework, gives no specifics for constituting a coalition government.

The leader of the northern rebels, Guillaume Soro, said his followers want seven government posts, including the top jobs in the defense and interior ministries. "There is no reason for these positions to be discussed," Soro said in a telephone interview from his northern stronghold of Bouake. "They should be granted to us."

Unless their demands are met, rebel leaders said they would overrun Abidjan, the commercial capital.

There was no mention of further implementation of the peace accord during the ceremony at the Hotel President, a faded symbol of the country's former role as West Africa's economic powerhouse. The former French colony, the world's top cocoa producer, was long the oasis of prosperity and peace in the region -- a place where immigrants from such countries as Liberia, Burkina Faso and Sierra Leone sought refuge and employment in the lush timber and cocoa fields.

But since the fighting began in the wake of a Sept. 19 coup attempt, thousands have been killed and about 1 million displaced, some of them forced to walk across the country with their belongings. Immigrant shantytowns were burned and foreigners were attacked by pro-government forces. Gbagbo, facing opposition to the accord among his own supporters, has moved cautiously to adopt peace measures.

There had been a lull in fighting after the French-brokered agreement was reached, but concerns that the accord was collapsing were underscored by government reports of battles with rebels in the west.

The event today, however, was a gleeful, pomp-filled affair. The president pumped his hands in victory as he stood on a red carpet. A troupe of child dancers performed as men wearing powder-blue suits, festooned with shiny gold buttons, played horns and drums.

Ivory Coast President Laurent Gbagbo, right, talks with Seydou Diarra, an opposition leader who was named prime minister as part of a peace deal. Female rebels patrol about 20 miles from the city of Man, in western Ivory Coast. Rebels have warned of a return to war by Friday.