At least 60 people have been killed in Central African Republic in fighting between former rebels and forces loyal to the president they ousted in March, officials say.
A government spokesman said fighters loyal to Francois Bozize had seized the town of Bouca north of the capital.
This is the first large-scale operation launched by the former president's forces since he was toppled in March.
The UN has warned that CAR could become a failed state, threatening the region.
Presidential spokesman Guy-Simplice Kodegue said bridges had been destroyed and villages attacked near the town of Bossangoa, 250km (155 miles) north-west of the capital, Bangui.
He accused pro-Bozize fighters of attacking members of the Muslim population.
The Seleka rebels who seized power in March are seen as largely Muslim.
Mr Kodegue said five Seleka fighters had been killed during the clashes.
It has not been possible to verify this information because of a lack of communication with the region.
Aid workers have accused undisciplined Seleka fighters of looting the healthcare system, as well as robbing civilians, since they came to power.
About a third of the country's 4.6 million people need assistance with food, shelter, healthcare or water, according to UN humanitarian chief Valerie Amos, who recently visited the country.
Last week, the authorities launched a disarmament campaign in Bangui.
CAR has gold and diamond deposits but has been unstable since independence.
Seleka leader Michel Djotodia, who was sworn in as president earlier this month, has promised to relinquish power after elections scheduled for 2016.
Mr Bozize is currently in France after initially fleeing to Cameroon when Seleka fighters seized Bangui.
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