NAIROBI — A mass grave was discovered on Monday in Kenya's Tana River region which has been rocked by three weeks of fighting between the Pokomo and Orma ethnic groups, police said.

More than 100 people had so far been reported killed since the latest round of violence erupted in mid-August, pitting the Pokomo farming community against their Orma pastoralist neighbours.

"We discovered a mass grave where we believe more people could be buried," said a police officer in the area who requested anonymity.

"We do not know who is buried in it, but from the look of things there could be more people" who were killed in the conflict than initially announced, he said.

Coast Province Police Chief Aggrey Adoli confirmed the discovery, saying a court order would be sought to enable security forces to exhume the bodies.

The grave was found in the Garsen area, the location of recent killings.

Clashes between the two groups have often been attributed to disputes over water and grazing rights. But locals say the recent surge of violence is also being fuelled by politics.

Fresh violence rocked the Tana River region late Sunday and early Monday, with at least 20 houses torched in two villages, the Red Cross said.

The villages were abandoned, because of the recent spate of violence and no casualties have been recorded.

More than 1,000 paramilitary police are to be deployed to the region.

The latest clashes have evoked the large-scale ethnic violence that erupted in the aftermath of Kenya's disputed 2007 polls.

The blood-letting at the time revealed the fragility of a country that had long been considered a bedrock of stability in the region, and some observers fear a surge in violence ahead of elections due in March 2013.

Last week Dhadho Godhana, assistant livestock minister and MP for Galole in the Tana River delta, was charged in court with incitement to violence.

Last month Kenya Red Cross chief Abbas Gullet said that more than 200 people had been killed countrywide in ethnic clashes since January.

Many of the attacks -- often tit-for-tat raids between rival ethnic groups in remote and impoverished rural areas -- generate little attention.