More than 100 people have so far been reported killed since the latest round of violence erupted in mid-August pitting the Pokomo, a 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 Provincial Police Chief Aggrey Adoli confirmed the discovery of the mass grave, saying a court order will be sought to enable the security forces to exhume the bodies.
"The only way they can be known is through exhumation which can only be done through the court's permission," he added.
The mass grave was discovered within the Garsen area where recent killings took place.
Clashes between the two groups have often been attributed to disputes over water and grazing rights.
But locals say the recent surge of violence - in which more than 100 people have officially been killed in less than a month - is also being fuelled by politics.