BUJUMBURA (Reuters) - Burundi's ruling party failed on Friday to win parliamentary approval for constitutional changes, which critics say would undermine a delicate ethnic power-sharing deal, after its junior coalition partner boycotted the vote.
Proposed constitutional amendments have stirred the worst political crisis in the east African country since a 12-year civil war ended in 2005, and raised fears of new turmoil.
The changes would include a single powerful prime minister from the ruling party replacing two vice president posts shared between the majority Hutu and minority Tutsi ethnic groups - a step opponents say threatens to marginalise minorities.
They may also pave the way for Burundi's president, Pierre Nkurunziza, to run for a third term in office.
Foes of Nkurunziza, an evangelical Christian popular among rural voters, view such reforms as a manoeuvre to consolidate Hutu power that will upset power-sharing requirements that have kept ethnic tensions in check since the war.
Interior Minister Edouard Nduwimana shrugged off the Hutu-led CNDD-FDD party's failure to muster enough votes in the national assembly, saying the amendments would be put to a referendum instead.
"When members of parliament fail to agree on constitutional reform, the president may submit the draft amendments to a referendum," Nduwimana told reporters in Bujumbura.
Burundi's political stand-off has raised the spectre of another explosion in a volatile region already grappling with unrest in eastern Democratic Republic of Congo, South Sudan and the Central African Republic.
The CNDD-FDD, which holds 81 out of 106 seats in parliament, fell one vote short of the 85 required to pass the amendments.
A Burundi court handed down life jail terms on Friday to 21 members of the opposition MSD party who clashed with police two weeks ago. The opposition says an arrest warrant for the leader of the MSD is an attempt to remove rival voices before elections in 2015.
The constitutional dispute has driven a wedge between the CNDD-FDD and its junior governing partner, the Tutsi-led Uprona party, whose leadership believes Nkurunziza is manoeuvring to stand for a third term.
Burundi's current basic law, which dates back to the end of the civil war, says the president can serve two directly-elected terms. A separate clause says the first post-war leader will be indirectly elected by lawmakers - as Nkurunziza went on to be.
Under the planned changes, the latter clause would be deleted. Stalwart allies of Nkurunziza argue that would allow the president to run again.
Agathon Rwasa, the last rebel commander to lay down arms in 2009 who last month told Reuters Nkurunziza was behaving increasingly like a dictator, said he held little hope for a credible referendum.
"They want to organise a referendum just to rig as they rigged 2010 elections," Rwasa told Reuters on Friday, referring to the last presidential vote he and others boycotted.
Writing by Richard Lough; Editing by Mark Heinrich