JOS - U.S.-based Human Rights Watch on Tuesday urged Nigeria to prosecute those behind what it called a massacre of at least 200 Christian villagers and end a cycle of impunity which has allowed instability to persist.

Residents of Dogo Nahawa, about 15 km (9 miles) south of the central city of Jos, buried dozens of bodies including those of women and children in a mass grave on Monday following weekend attacks on three communities by Muslim herders.

The rights group called on Acting President Goodluck Jonathan, who promised after unrest around Jos in January that those responsible would be brought to justice, to ensure a credible investigation and prosecutions.

Police spokesman Mohammed Lerama said 93 people had been arrested.

Jonathan deployed troops to quell January's unrest and a dusk-to-dawn curfew was still in place when Sunday's attack took place. Human Rights Watch said the military deployment had been limited to major roads and failed to protect small communities.

Residents of Dogo Nahawa, Zot and Ratsat, all predominantly Christian settlements, said Muslim herders from surrounding hills attacked in the early hours of Sunday, opening fire to force them from their homes before slashing them with machetes.

Some died as they tried to flee, others were burned alive.