(Adds Akayev's reaction)

By Olga Dzyubenko

BISHKEK, Feb 14 (Reuters) - Kyrgyz President Kurmanbek Bakiyev's main revolutionary ally switched sides on Wednesday, accusing Bakiyev and his allies of corruption and saying he would unite and lead the volatile nation's scattered opposition.

Felix Kulov's dramatic announcement risked sparking new tension in the impoverished Central Asian nation, home to both a U.S. and a Russian airbase, after mass street protests last November almost forced Bakiyev to resign.

Kulov, a former security boss, was sprung from jail during the March 2005 "revolution" and teamed up with Bakiyev to help oust long-serving leader Askar Akayev.

Bakiyev, a southerner, and Kulov, a northerner, ran on a joint ticket after Akayev's ouster in a symbol of unity in the ethnically divided nation, becoming president and prime minister -- though Kulov has since quit as premier.

"I have decided to ... unite and head all the fragmented but friendly political forces -- all those who want radical and positive change," Kulov told reporters, diplomats and political allies. "I cannot and will not just stay an observer."

Kulov, who resigned in December to ensure a new constitution went into force, said he was angry with Bakiyev for failing to help him regain his post and nominating another candidate.

Bakiyev's office said it had honoured the terms of its partnership with Kulov. "(Kulov) has his own interpretation of the situation that arose. That is his right," it said in a statement.

Bakiyev tried to reinstate Kulov as prime minister but gave up after parliament twice voted against his proposal.

RIFT

Kyrgyzstan, an ex-Soviet state bordering China, has been increasingly volatile since Akayev's ouster.

Akayev, now in exile in Russia, said tension was rising among various clans and ethnic groups in his country, whose political culture is based largely on tribal and personal ties.

"There is a rift between the north and the south in Kyrgyzstan, between pro-Bakiyev and anti-Bakiyev people. Inter-ethnic conflicts are on the rise," Akayev told reporters.

"There is talk about a new wave of protests this spring. I am against protests ... Our nation will not survive another revolution. It will fall apart."

Bakiyev won a presidential election by a landslide in 2005, pledging to bring law and order and raise living standards. The opposition says he has failed to carry out his promises, and has staged many mass protests calling on him to resign.

Kulov did not call for a change of leadership, but some politicians saw his announcement as a call to arms.

"Of course there will be a certain level of panic in the White House," opposition politician Anvar Artykov told Reuters, referring to the government headquarters. "The authorities may resort to force to settle any crisis."

Another opposition MP, Melis Eshimkanov, added: "We have to get rid of our personal ambitions. ... (Kulov) can be our flag."

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