* UN says most trapped are Muslims, under threat
* More violence in Bangui, two looters killed
* French parliament to vote on troops extension
By Serge Leger Kokpakpa
BANGUI, Feb 25 (Reuters) - Over 15,000 people in Central African Republic, mostly Muslim civilians in makeshift camps, are surrounded and being threatened by armed militia groups, a spokesman for the U.N. refugee agency said on Tuesday.
Adrian Edwards told a news briefing in Geneva that the refugees, dotted around 18 locations in the northwest and southwest of the landlocked country, face a high risk of attack and urgently need better security.
France's parliament voted in favour on Tuesday of extending its military mission in Central African Republic, Operation Sangaris, four months after its launch.
The former French colony has been torn by inter-communal violence that has killed thousands since Seleka, a coalition of mostly Muslim northern rebels, seized power in March and unleashed a wave of looting and killings.
Christian militia known as "anti-balaka", which means "anti-machete" in the local sango language, have exacted brutal reprisals against the Muslim minority whom they accuse of supporting the rebels. Ten of thousands of Muslims have fled to neighbouring countries, while others sought shelter in camps.
"Although violence has hit all communities in CAR, most of the people who are trapped are Muslims under threat from 'anti-balaka' militiamen," Edwards said. "Areas we are particularly worried about include the PK12 neighbourhood in Bangui and the towns of Boda, Boar and Bossangoa."
Tit-for-tat killings have continued despite the presence of 2,000 French and 6,000 African Union peacekeepers (MISCA). Aid workers say security has improved somewhat in the capital Bangui in recent weeks, though sporadic attacks continue.
Burundian peacekeepers shot dead two anti-balaka fighters who were looting a shop in Bangui on Tuesday, witnesses said.
In Carnot, a town of about 45,000 some 500 km (310 miles) northwest of the capital, Muslims sought protection at a local church after hiding in the bush for several days.
Priest Justine Nary said that over 1,000 people, many of them women and children, had sought refuge in Carnot's church.
Nary said the mood was tense after anti-balaka militia threatened to torch the building if Muslims did not leave, despite the presence of AU and French troops.
"We received 223 more people this morning and the truck has gone out again to fetch more people from the bush where they are hiding," he said.
The crisis has driven around 1 million people - about a quarter of the country's population - from their homes. Many of them have fled to neighbouring Cameroon, Chad, Democratic Republic of Congo and Republic of Congo.
The World Food Programme warned on Tuesday that the exodus could spark a regional crisis as countries struggled to accommodate the refugees.
Despite some lawmakers concerns about how the mission has been handled, French members of parliament voted on Tuesday massively in favour of extending the mission in the country, with only a hand-full abstaining or voting against.
In France, a foreign military operation requires parliamentary backing when it lasts more than four months.
"Everyone is aware that our job is not finished," Prime Minister Jean-Marc Ayrault told lawmakers. "Our efforts have started to bear fruit. The threat of a widespread flare-up was avoided."
Some opposition lawmakers have accused French President Francois Hollande of miscalculating the situation in Central African Republic, demanding to know how long French troops will stay and the cost of the mission.
"The president has been careless," the head of the opposition UMP party in the lower house, Christian Jacob, said during a debate in parliament. "This carelessness has led, as we feared, to an impasse, a trap which we don't see how to get out of." (Additional reporting by John Irish and Emile Picy in Paris, Stephanie Nebehay in Geneva and Bate Felix in Dakar; Writing by Bate Felix; Editing by Mark Heinrich)
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