Bangui - More than 100 people have been killed in fierce fighting in the past 10 days in the Central African Republic, as charity Doctors Without Borders said it would reduce its work after a bloody attack on a hospital.
Among the dead were many civilians, with one eyewitness claiming children had been thrown alive onto fires.
Some 75 people died in fighting close to the country's northern border with Chad, an official with the African peacekeeping force said on Monday.
The clashes pitted fighters from the former rebel Seleka coalition against members of the Fulani tribe, the source said on condition of anonymity.
Around 55 people were killed near the town of Paoua, while another 20 people perished near Markounda, said a military official. Both towns are located close to the border with Chad.
The official added that the killings were carried out over a period of "several days" in an area patrolled by armed fighters from the Seleka rebels and the Fulani tribe.
"They attacked nearly 10 villages around Markounda between Wednesday and Friday. They also attacked more than 40 villages near Paoua on the Chadian border," said the same source.
One anonymous source told AFP by phone that the death toll could rise.
"The atrocities committed by these armed men are indescribable."
One resident of Markounda, Yetina Isaac, described how rebels attacked by banging "doors, shooting the occupants and then setting houses on fire".
"The injured and helpless perished and burned alive, while the bodies of those already dead were also burnt."
Isaac added that she saw children being "thrown alive on the fire".
News of the deadly clashes in the north came as it was announced that almost 30 people were also killed in fighting in the Mala region, some 200km north of the capital Bangui.
The deaths there were a result of fighting between Seleka rebels and the Christian vigilante groups known as the anti-balaka, another official from the African peacekeeping force MISCA told AFP, with locals forced to flee to neighbouring areas.
Residents told AFP by phone that Seleka fighters still occupied Mala and were committing atrocities.
"They kill, loot, rape and steal with impunity. There is no one to protect the population from their abuses. Even the Catholic Church in Mala was attacked and those seeking refuge inside were fired upon and had to flee," said Eric Ketegaza, one of those who fled Mala.
The militias were formed last year in response to the coup by the Seleka rebels that toppled president Francois Bozize.
In a sign that the situation in the country was deteriorating, international charity Doctors Without Borders (MSF) said on Monday it would temporarily cut back its work in the country after a bloody attack on a hospital last month left 22 people dead, including three of its own workers.
"In protest against the brutal killing of 16 civilians, including three of its humanitarian workers at Boguila Hospital on 26 April, MSF is reducing its activities in CAR and related projects in neighbouring countries for one week to emergency medical care only," it said in a statement.
MSF also expressed shock that the transitional government and spokespeople for armed groups failed to publicly condemn the massacre and other daily atrocities.
The landlocked and deeply poor country descended into conflict after a March 2013 coup by mainly Muslim rebels of the Seleka alliance, who seized power for 10 months.
Many of the ex-rebels eventually went rogue, targeting civilians and their property in vicious attacks that displaced hundreds of thousands.
In response, mostly Christian vigilantes known as "anti-balaka" were formed, going on to kill and terrorise Muslims.
France has deployed about 2 000 troops to back the 6 000 Africans of the MISCA force.
Currently around 8 000 international troops are working to contain the crisis in the former French colony, which has left tens of thousands dead and displaced around a quarter of the country's 4.6 million people. This is expected to increase to 12 000 in September.