Up to 37 people including women and children were killed in Democratic Republic of Congo's eastern province of South Kivu on Saturday in an attack that government officials blamed on a dispute over cattle.
The victims, who included several pregnant women, had been shot, stabbed or burned inside their homes. A Reuters cameraman on the scene in the village of Mutarule counted 37 bodies, some of them lying inside a village church.
Residents and religious leaders said patients in a medical centre had also been attacked. Apart from the dead, more than 20 people were injured, with 10 of them in critical condition.
"It is Congolese who have carried out these attacks. It was about a dispute over cows," South Kivu governor Marcellin Cishambo told Reuters. "The problem is that everyone in this area carries a weapon."
He gave a lower estimate of 27 for the number of dead.
Government spokesman Laurent Mende said the incident was a revenge attack by the community of a cattle herder killed during an attempt to steal cows belonging to another farmer.
"The army commander (in the locality) has been arrested because he reacted too slowly. He is now with military police. Authorities also arrested a local leader suspected of coordinating the attacks," Mende added.
He said 34 people had died in the violence.
South Kivu, a mountainous region rich in minerals including gold, is home to members of tribes who fled neighbouring Burundi after the end of a civil war in 2005 as well as numerous rebel groups, including the Democratic Forces for the Liberation of Rwanda (FDLR).
Some locals from the Congolese Bafuliru tribe blamed rebels from Burundi's National Liberation Forces (FNL) for the attacks. Residents said that last August eight people had been killed by unidentified armed men in the same village; a concrete grave with eight small crosses marks their final resting place.
"The first massacre took place, then the second one has just happened - and we did not even get to know what happened with the first massacre," village elder Amuri Kikukama told Reuters.
"We wonder why the killings should go on while the government is watching."
A second resident said there an armed militia had a base about 20 km (12 miles) from the village. Many locals were packing their belongings on Saturday to move to another village.
Martin Kobler, head of the U.N. mission in Congo MONUSCO, said it was sending reinforcements to protect the population.
"These violent acts are unacceptable and need to stop immediately," he said in a statement.
The Congolese government has said it plans to target foreign rebels operating in its eastern region after the defeat of the M23 rebel group late last year.