Red Cross on Wednesday said its workers had found 115 bodies in the Central African Republic's (CAR) border town of Bangassou after several days of militia attacks, raising by more than four times a previously reported death toll.
Antoine Mbao Bogo, the president of the aid group's local branch, told the Reuters news agency that those killed had "died in various ways", including from knives, clubs and bullet wounds.
"We found 115 bodies and 34 have been buried," he said from the capital, Bangui.
A senior UN official had previously reported 26 civilian deaths.
According to the UN refugee agency, the situation in Bangassou sent an estimated 2,750 refugees fleeing across the border into the Democratic Republic of Congo (DRC) over the weekend.
The violence represents a new escalation in a conflict that began in 2013 when mainly Muslim Seleka fighters seized power and removed then-president Francois Bozize, prompting reprisal killings from Christian anti-Balaka militias.
The UN high commissioner for human rights warned on Tuesday the violence in areas previously spared major bloodshed was "highly worrying".
"The hard-earned relative calm in [the capital] Bangui and some of the bigger towns in CAR risks being eclipsed by the descent of some rural areas into increasing sectarian violence, with defenceless civilians - as usual - paying the highest price," Zeid Ra'ad al-Hussein said.
In a statement on Tuesday, Stephane Dujarric, spokesman for UN Secretary-General Antonio Guterres, also said unverifiable figures indicate up to 100 people may have been killed in three days of clashes from May 7 to 9 in the town of Alindao between anti-Balaka fighters and an ex-Seleka group.