Clashes between rival armed groups in the Central African Republic have left at least 16 people dead and displaced several thousand civilians, the UN said, warning of "targeted assassinations" against ethnic Fulani.
"There have been at least 16 confirmed death and thousands displaced," Vladimir Monteiro, spokesman for United Nations peacekeeping force MINUSCA, said in a statement.
The violence erupted on Monday between rival factions of the former "Seleka" Muslim rebel group in the town of Bria, 400 kilometers (250 miles) northeast of Bangui.
MINUSCA said Tuesday that one of its bases had come under fire during the clashes before its troops drove the attackers out with retaliatory gunfire.
It announced reinforcements were being sent to the base to protect some 5,000 civilians sheltering there.
The fighting broke out between the Popular Front for the Renaissance of the Central African Republic (FPRC) and the Union for Peace in Central Africa (UPC).
The two factions are fighting for control of taxes levied on Fulani herders during the current seasonal migration.
Lambert Lissane, a senior FPRC official, said the group and other ex-Seleka armed groups were negotiating a deal with the government but that UPC chief Ali Darass did not want to take part.
"We have decided to stand together against him," Lissane said.
The government is trying to bring together 14 armed groups under a disarmament deal to consolidate a fragile peace in the former French colony, where militias are flourishing in the power vacuum left by a weak state.
One of the world's poorest countries, CAR is struggling to emerge from a civil war which erupted in 2013 following the overthrow of former president Francois Bozize, a Christian, by Muslim rebels from the Seleka coalition.
The coup led to the formation of "anti-Balaka" vigilante units, drawn from the Christian majority, which began to target Muslims. Both sides committed widespread atrocities.
France last month withdrew a military mission it deployed in December 2013 to stabilise the country, leaving the UN's 12,500-strong MINUSCA peacekeeping mission to protect civilians from armed groups.
International donors last week pledged $2.2 billion (two billion euros) in aid for the strife-torn country.