* Burundi faces worst crisis since end of civil war
* Opposition leader accused of inciting unrest
* United States, France urge calm
By Patrick Nduwimana
BUJUMBURA, March 12 (Reuters) - Burundi's authorities have ordered the arrest of an opposition leader after clashes between his party members and police last week, a move the opposition said was a bid to remove rival voices before elections in 2015.
Agnes Bangiricenge, spokeswoman for Burundi's public general prosecutor, told Reuters an arrest warrant had been issued for MSD Chairman Alexis Sinduhije.
More than a dozen members of the opposition Movement for Solidarity and Democracy (MSD) party, part of the Alliance for Democratic Change (ADC), were injured in clashes with police on Saturday.
Witnesses said police tried to break up a party meeting. Officials say the party was stirring rebellion.
"Sinduhije is accused of participating in an insurgency movement and rebellion," Bangiricenge said, adding 50 MSD members were detained and their trial date would be fixed soon.
The east African nation is facing its worst political crisis since emerging from a 12-year civil war in 2005, worrying neighbours and Western donors that it could spark more unrest in an already volatile region of the continent.
Sinduhije could not be reached for comment. Party associates said he had gone into hiding after the warrant was issued.
The United States, a key donor, said it was worried by the use of heavy-handed tactics to break up the March 8 meeting, but also criticised MSD members who during the clashes captured two officers whom they accused of trying to disrupt the gathering.
Washington urged respect for the democratic process to allow for free and fair elections next year, though opponents of Nkurunziza have voiced little optimism for a transparent vote.
"We know for sure that this is an existing plan by the ruling CNDD-FDD party to exclude from competition any opponent who can pose a threat in the 2015 elections," said the chairman of the ADC opposition coalition, Leonce Ngendakumana.
Interior Minister Edouard Nduwimana said the MSD could be suspended for six months or scrubbed from a list of legal parties.
"What Sinduhije and his party did is unacceptable. We can't tolerate a party or a politician who promotes uprising," Nduwimana told a news conference.
The UN Mission in Burundi (BNUB), set up to assist in the political transition, called on Burundi's political leaders to avoid stoking tensions. France echoed the concerns of the United Nations and United States.
"We call on the Burundian authorities and the opposition to refrain from all violence and pursue dialogue with a view to general elections in 2015," foreign ministry spokesman Romain Nadal said on Tuesday.
Despite relative calm in recent years, rights groups have reported scores of political killings, intimidation of the opposition and a crackdown on the media since President Pierre Nkurunziza's re-election in 2010.
Critics say the president is planning a third term in office, although he has not said so. The president's opponents and supporters differ on whether the language of the constitution would allow him another term.
Tensions in Burundi have raised concerns of a new flare up in an area with conflicts smouldering in the eastern Democratic Republic Congo, South Sudan and the Central African Republic. Landlocked Burundi borders Rwanda, where Hutu extremists targeted ethnic Tutsis and moderate Hutus in the 1994 genocide. (Additional reporting by John Irish in Paris; Editing by Edmund Blair and Tom Heneghan)