At least 33 people have been killed in eastern Democratic Republic of Congo, in what appeared to be part of an ongoing ethnic conflict over land and cattle.

Sources told Al Jazeera that gunmen surrounded a church in the village of Mutarule late on Friday and started firing indiscriminately.

"We're hearing that most of the dead were women who were in the church," Al Jazeera's Catherine Soi, reporting from the eastern city of Goma, said. "Some other people were killed in their homes."

Eighteen women and eight children were reportedly among those killed. Some of the victims were stabbed or burned.

Human rights groups in the area told Al Jazeera that the attack was part of an ongoing conflict between pastoralists and farmers.

"They're also saying that this is poltiically motivated, that some politicians have been stoking ethnic tension in that part of South Kivu," our correspondent reported.

'Revenge attack'

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 problem is that everyone in this area carries a weapon. Marcellin Cishambo,

South Kivu governor

"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 said.

The UN mission in DR Congo (MONUSCO) late on Saturday issued a statement saying that "fierce fighting" had taken place the night before between the Bafuliru on one side and the ethnic Barundi and Banyamulenge on the other.

"This violence is unacceptable and must end immediately," said Martin Kobler, head of MONUSCO.

The Barundi and Banyamulenge are Tutsis originally from Burundi who have been living in South Kivu for generations.

There has been a conflict for a dozen years between the Bafuliru and the Barundi over property and custom issues.

UN peacekeepers have been sent to Mutarule to evacuate the wounded and help the local authorities and the Congolese army restore calm to the area.

Some locals from the Bafuliru tribe blamed rebels from Burundi's National Liberation Forces (FNL) for the attacks.

But South Kivu governor Marcellin Cishambo told Reuters news agency that it was "Congolese who have carried out these attacks".

"The problem is that everyone in this area carries a weapon," he said.