US-based Human Rights Watch has 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.
"This kind of terrible violence has left thousands dead in Plateau state in the past decade, but no one has been held accountable," said Corinne Dufka, senior West Africa researcher at Human Rights Watch. "It's time to draw a line in the sand."
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.
Mr 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.
A witness counted more than 100 bodies on Sunday in Dogo Nahawa alone. Plateau State Commissioner for Information Gregory Yenlong has said 500 people died but the official police death toll is 55, with bodies still being counted.
Death tolls have been highly politicised in previous outbreaks of unrest in central Nigeria, with various factions accused of either exaggerating the figures for political ends or downplaying them to try to douse the risk of reprisals.
The latest violence in the centre of Africa's most populous nation comes at a difficult time for Jonathan, who is trying to assert his authority while ailing president Umaru Yar'Adua remains too sick to govern.
The instability underscores the fragility of Africa's top energy producer as it approaches the campaign period for 2011 elections with uncertainty over who is in charge.
UN secretary general Ban Ki-moon called on political and religious leaders to find a "permanent solution" to the crisis in Jos. The United States urged the government to ensure those responsible faced justice in a "transparent manner".
Witnesses said Sunday's attack appeared to be a reprisal for January's unrest, four days of clashes between Christian and Muslim mobs which killed several hundred people, including many in an attack on the mostly Muslim settlement of Kuru Karama.
Plateau state lies at the crossroads of Nigeria's Muslim north and Christian south and fierce competition for control of fertile farmlands between indigenous groups and settlers from the north have repeatedly triggered unrest over the past decade.
Local officials said many of those responsible for January's violence were the same people arrested but not prosecuted after similar unrest in November 2008.
More than 300 people were arrested in January and about half of them were due to be sent to the capital Abuja for prosecution, but it is unclear how many actually faced justice.
Many of Nigeria's prisons are overcrowded and the legal system overburdened with cases. It is not uncommon for communities to punish criminals themselves and blame their actions on the country's weak judicial system.
Reuters