"The overall situation needs to be taken seriously," warned E.J. Hogendoorn, acting Africa program director of the International Crisis Group, amid mounting anxiety.
"If it were to deteriorate significantly, especially along Christian-Muslim lines, it could have grave repercussions for national cohesion in the buildup to national elections in 2011."
Religious violence erupts periodically in Nigeria's "middle belt" along the north-south boundary, although the root cause is often disputes over land and political rivalry.
The government of Plateau state in Jos, the capital and long the epicenter of the religious clashes, is controlled by Christians who have blocked Muslims from being legally recognized as citizens, blocking them from government employment.
In the latest spasm of violence, four bombings last Friday around Jos killed 32 people and wounded 74.
Another six people were killed in attacks on three churches in Maiduguri, 320 miles northeast of Jos and capital of Borno state, by suspected members of an Islamist sect known as Boko Haram. That means "Western education is sacrilege" in the regional Hausa language.
Boko Haram has been blamed for a series of attacks over the last few years in which several thousand people have perished. In the last major flare-up in July 2009, more than 700 people were killed on both sides in clashes triggered by a disputed local election. Another 320, mostly Muslims, were killed in January in and around Jos.
Local human rights groups claim about 1,500 people have died in inter-communal bloodshed over the last year in the region.
There are widespread suspicions that politicians have stoked religious and ethnic divisions ahead of the primaries, which will precede presidential elections in April.
Nigeria's population of around 150 million is divided almost evenly between Christians and Muslims. Under a power-sharing pact when a 15-year military dictatorship ended in 1999, north and south alternate holding the presidency for two four-year terms.
The death in May of President Umaru Yar'Adua, a northerner, during his first term triggered a power struggle between the political barons in north and south. For months, while Yar'Adua was treated in a Saudi Arabian hospital, Nigeria was in political limbo because the ailing president hadn't designated a successor and for a time no one appeared to be in control.
Yar'Adua was eventually succeeded by his vice president, Goodluck Jonathan, a southerner who is running a controversial campaign ahead of the primaries.
If he succeeds in winning re-election, the north-south political pact could end up in shreds.
Already there are fears that the unrest gripping Nigeria, including an insurgency in the oil-rich south that has slashed oil production by about 40 percent, will be exploited by the rival political groups.
The oil industry, centered largely in the swamplands and creeks of the Niger Delta on the Atlantic coast, provides 90 percent of Nigeria's state revenue. The country is the United States' fifth largest oil supplier.
The instability underlined Nigeria's fragility as the country approaches the elections.
"In the buildup to the 2011 national elections, the worst-case scenario is that local violence (in the north) will polarize the rest of the country," the ICG cautions.
"While some in the West panic at what they see as growing Islamic radicalism in the region, the roots of the problem are more complex and lie in Nigeria's history and contemporary politics," observed the ICG's West Africa specialist Titi Ajayi.
The central government's failure to maintain public order, decades of economic neglect in the Muslim north and the "political manipulation of religion and ethnicity" have all contributed to the current instability, the ICG maintains.
Boko Haram has been reported to have links with al-Qaida in the Islamic Maghreb, or North Africa, although so far there has been no concrete evidence of that.
But the ICG observes that "while a thread of rejectionist thinking runs through northern Nigerian history, according to which collaboration with secular authorities is illegitimate … calls for an Islamic state in Nigeria should not be taken too seriously, despite media hyperbole."