WASHINGTON (CNN) -- Kenya's new power-sharing deal is a "critical step toward the legitimate government of the country," U.S. Assistant Secretary of State Jendayi Frazer said Thursday, pledging the United States would keep the parties "on the right track."
Political rivals Kibaki and Odinga have agreed to form a coalition government
Opposition leader Raila Odinga had demanded the creation of a prime ministerial position, with real power and got it in the deal announced Thursday in Nairobi.
Odinga had accused the government of President Mwai Kibaki of stealing last year's Presidential elections.
Frazer told CNN this deal will create a "positive spirit" for Kenya's political leaders to tackle tougher issues, like rewriting the constitution and redistributing land.
Throughout the month-long negotiation process between Kenya's president and opposition leader, the United States has staunchly backed the Koffi Annan mediation efforts.
Secretary of State Condoleezza Rice travelled to Kenya to give him a boost and to insist that Kenyan leaders make a genuine compromise with no excuses for a delay. Frazer said the U.S. voice was "decisive in helping them to realise that the only solution would have to be a compromise."
She acknowledged that hardliners on both sides who may be unhappy with the agreement may try to sabotage it but it would be "difficult" to undermine a legal and constitutional document.
"Clearly in the process of implementation we can expect there will be some types of disagreement," she said. "These are two parties and in fact two men who have disagreed fundamentally."
Frazer said the United States and the rest of the international community will "keep them moving on the right track."
More than 1,000 people have been killed and up to 600,000 displaced since December last year. The United States has called for justice, and Frazer reinforced that demand Thursday.
"You can't have a thousand people die, innocent people die, and no one be held accountable. But that process, as this political deal, will be an international one," she said.
Once bitterly divided, President Kibaki and opposition leader Raila Odinga were shown on Kenyan television Thursday sitting together at a desk during a public ceremony and signing the deal in front of a crowd.
Odinga said: "We on our side are completely committed in ensuring that this agreement will succeed. The ball has moved partially from the hands of the negotiators and ourselves to the court of parliament."
Kibaki said that his government "will fully support implementation of the agreement reached under the national dialogue and reconciliation process until we achieve the results we all want."
The agreement calls for an act of parliament within two weeks that would change the country's constitution, creating the position of prime minister to "coordinate and supervise" the government and its ministries. Odinga will assume that position.
The National Accord and Reconciliation Act 2008 establishes that the president, vice president, prime minister and other ministers will form the government's cabinet -- with the addition of two deputy prime ministers who will be appointed by the president.
The act also stipulates that ministers cannot be fired without written permission from their party.
Former U.N. Secretary-General Kofi Annan , who served as the chief mediator in the process, stood behind the men, at times showing a faint smile as they signed the deal.
Annan said: "They kept the future of Kenya foremost in their sights. Let the spirit of healing begin today. Let it start now. Compromise was necessary for the health of this country."
Odinga thanked Kibaki and recognized him as president. He conceded that they had been competitors but are now "countrymen."
"In the past two months, Kenyans have known nothing but sadness," he said. "May we dwell in liberty and peace and unity. I will assure that what we have developed today will succeed."
Kibaki urged Kenyans to forget the violence of the recent weeks.
"We must all do our part to safeguard our peace. That is the foundation of our nation," he said. "Kenya has room for all of us if we can enhance peace and tolerance. Fellow Kenyans, we stand before you to give a solemn commitment."
The tense negotiations were initiated in the wake of violence after the disputed presidential election on December 27 in which Kibaki, the incumbent, was declared victor.
Kibaki's win was immediately called into question, with election observers from the European Union saying they doubted the legitimacy of the count. Analysts said it was probable that both of the main parties had been involved in electoral fraud.
Violence erupted, with fighting breaking down along tribal lines. Members of Kibaki's Kikuyu tribe and the Luos, the tribe of Odinga, have been in the middle of the ethnic clashes.
Hundreds have been killed and more than 300,000 have been displaced since the post-election violence started, according to the Kenya Red Cross. E-mail to a friend
CNN's David McKenzie contributed to this report