* Ethnically fuelled civil war ended in 2005
* Presidential race scheduled for June 26
* Ruling party tells police to deal with protesters (Adds U.S. comment)
By Patrick Nduwimana
BUJUMBURA, April 25 (Reuters) - Burundi's ruling party chose President Pierre Nkurunziza to run for a third five-year term on Saturday, a move critics say is unconstitutional and may trigger unrest in the East African country.
Opposition groups promised protests if Nkurunziza runs, saying it would undermine a peace deal that has kept the country calm for a decade since an ethnically-fuelled civil war ended in 2005.
Two months before the presidential election, Nkurunziza, 51, was nominated at a meeting of nearly 1,000 members of his party, which grew out of a Hutu rebel movement.
"No one will stop the CNDD-FDD party," the president declared.
"I call people to go to the election in peace," he said after the decision. "But I would like to warn everyone: whoever wants to create problems with the ruling party elected by the people, he'll find himself in trouble."
Party chairman Pascal Nyabenda urged the police and security forces to take action against any street protests.
Any flare-up in Burundi threatens broader repercussions. It could draw in neighbouring Rwanda, where 800,000 mainly Tutsis and moderate Hutus were killed in a 1994 genocide, and create turmoil in a region where other presidents, including Joseph Kabila in Democratic Republic of Congo, are nearing the end of their constitutionally defined term limits.
Burundi's Constitution says the president is elected for a five-year term, renewable only once. But Nkurunziza's supporters say his first term should not count because he was chosen by parliament rather than having been voted into office.
"DESCEND ON THE STREETS"
The ruling party says it will be up to the constitutional court to hear any appeals against its candidate. Opponents say they do not trust the courts to give them a fair hearing.
"Once Nkurunziza is declared the candidate, we won't wait. The next day, over 300 civil organisations engaged in a campaign against a third term for Nkurunziza will descend on the streets," prominent civil society activist Pierre Claver Mbonimpa told Reuters before the nomination was announced.
Opposition politician Agathon Rwasa urged anyone protesting to avoid violence, but said he was not calling for demonstrations now to avoid giving the ruling party a reason to "harass and persecute people."
He also called on countries in the region as well as international powers to put more pressure on the president to step aside.
Some opposition supporters staged street protests earlier this month, including on April 17 when demonstrators scuffled with police. Any clampdown on rallies could stoke tensions in a country which has suffered from decades of ethnic violence.
African leaders and Western nations have been pushing Nkurunziza not to run. The United States and the European Union indicated they could take steps if violence erupted.
The United States said it deeply regretted the decision by the ruling party to name Nkurunziza as its candidate again, urged all parties to take part in the upcoming elections and warned it would sanction those who took part in any violence.
Acting U.S. State Department spokeswoman Marie Harf issued a statement saying all parties should "refrain from any violent acts, including hate speech or other provocations, that could feed the climate of fear and instability."
It also praised Burundi's neighbors for helping "almost 15,000 Burundians who have fled the country over the past month."
The United States would "take targeted measures, including, where appropriate, by denying U.S. visas, to hold accountable those individuals" who insitigate or take part in violence, the statement said.
Burundi's civil war pitted the army, then dominated by the ethnic Tutsi minority, against rebel groups mostly of the majority Hutus. The army now includes both ethnic groups and has absorbed rival factions, though experts fear it could fracture if tensions rise. (Additional reporting by Edmund Blair in Nairobi; writing by George Obulutsa and Edmund Blair; editing by Mark Trevelyan, G Crosse)
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