(Refiles to say ministers appointed on Tuesday in par 7)
* Standoff deepens political uncertainty
* Burundi facing worst political crisis since end of war
By Patrick Nduwimana
BUJUMBURA, Feb 18 (Reuters) - Burundi's president appointed three ministers from his junior coalition partner in a bid to end a political crisis on Tuesday, but a rival group in the party rejected the candidates and said it no longer considered itself part of the government.
The standoff added to the political uncertainty in the tiny East African country, led by a complex power-sharing government set up to contain ethnic tensions between majority Hutus, Tutsis and other groups.
Political wrangling in the country, which emerged from a 12-year civil war in 2005, has raised the spectre of more unrest in a region already grappling with violence in eastern Democratic Republic of Congo, South Sudan and the Central African Republic.
Landlocked Burundi also borders Rwanda where Hutu extremists targeted ethnic Tutsis and moderate Hutus in the 1994 genocide.
Members of Tutsi-led UPRONA party, the junior member of the government, have accused President Pierre Nkurunziza, a Hutu, of trying to change the constitution to undermine the power-sharing deal and extend his grip on power. Nkurunziza has not commented on the accusations.
Three UPRONA ministers quit the coalition earlier this month after the president sacked his Tutsi vice president, also from UPRONA, triggering the worst political crisis since rebels laid down their arms.
President Nkurunziza has since appointed a new deputy from UPRONA and on Tuesday appointed three other UPRONA members to replace the three ministers.
But rivals in UPRONA rejected all the new candidates, saying they did not represent the mainstream membership and had been chosen because they would support the president's policies.
"We do not recognise the three ministers because they were not appointed by UPRONA leadership," UPRONA deputy chairman Evariste Ngayimpenda told Reuters.
"UPRONA is not part of this government, which is unconstitutional... Today there is no coalition government, but government made only by the (president's Hutu-led) CNDD-FDD party."
Ngayimpenda said the three ministers were sent to the presidency by a smaller wing of UPRONA which has been created to satisfy the interest of the ruling party.
The party would challenge all the new appointments at the country's constitutional court, Nkurunziza added.
The president's spokesman said the appointments had followed all the rules set down in the constitution.
"The head of state has completed its cabinet team to respect ethnic balance," said Leonidas Hatungimana.
Presidential and parliamentary elections are due in 2015.
"The President's CNDD-FDD party, UPRONA and other opposition parties need to sit down and find a lasting solution to the current crisis for the sake of peace and free and fair elections," said Gertrude Kazoviyo, a Burundi State University lecturer and political analyst.
The turmoil deepened on Sunday when riot police clashed with members of UPRONA who were attending a meeting to vote on party leaders, firing teargas to disperse the crowd.
Burundi's army - whose leadership is also split under the same arrangements as the power-sharing government between Hutus and Tutsis - said on Monday it would not intervene in the crisis, and would remain neutral. (Writing by James Macharia; Editing by Andrew Heavens)