At least 40 people have been killed in fighting in the Central African Republic (CAR), a day after a ceasefire was signed between rebels and the government.
The mayor of the town of Bria, north-east of the capital, Bangui, spoke of bodies lying in the streets.
The truce, signed in Rome on Monday, included an immediate ceasefire.
It was intended to bring armed groups into the political process in exchange for ending attacks.
Thousands of people have been killed and hundreds of thousands displaced in the CAR since mainly Muslim Seleka rebels ousted President Francois Bozize in 2013.
The move triggered a backlash from mostly Christian militias, called the anti-balaka.
Aid agency Medecins Sans Frontieres said fierce fighting erupted in Bria early on Tuesday.
Town Mayor Maurice Belikoussou told Reuters news agency that 42 bodies had been taken to hospital.
"There are also bodies in the neighbourhoods that have not been picked up yet," he added.
The peace agreement was brokered by the Sant' Egidio Catholic Community in the wake of years of sectarian violence and the deployment of a long-running UN peacekeeping mission in the country.
More than a dozen militia groups agreed to end hostilities immediately and to co-operate with a truth, justice and reconciliation commission.
But observers say armed groups have yet to show an interest in laying down their arms.