Authorities sealed off a northern Nigerian state hit by Muslim-Christian violence, and warned communities across the state Sunday to be on guard against the conflict's spread.

Residents of the 4 million-resident city of Jos, contacted by telephone, said the killing was persisting for a third day, despite deployment of the army Saturday.

Rival Christian and Muslim gangs were playing cat-and-mouse with police and troops, singling out targets of opposing faiths and killing them when security forces were not around, residents told The Associated Press.

The pace of the killing appeared to have slacked off from its peak Friday and Saturday, when witnesses said gangs were battling in the streets with guns, machetes and clubs. One man alone, in a telephone interview with AP, admitted helping kill 10 people at a makeshift roadblock.

With residents still fearing to venture out, only two churches held Sunday services, after two other churches were burned. Muslims tried to attack one Sunday service but were turned back by police, residents said.

Clashes were reported on the city's outskirts as well, and at least two killings were reported elsewhere in Plateau state, where Jos is located. With tensions high statewide, it was feared those killings were also religiously motivated.

After initially describing the situation as calm Sunday morning after a 4 p.m. to 6 a.m. curfew, officials at midday were refusing comment on the violence.

State police commissioner Mohammed Abubakar confirmed that unrest continued Sunday, but refused to discuss the fighting or possible death toll.

The priority now was securing lives and property, Abubakar said.

The violence in Jos broke out Friday night at the time of Muslim prayers. Some residents said it started when a Christian woman tried to cross a street were Muslim men were gathered to pray.

The violence was the latest since the introduction of Sharia, or Islamic law, in several northern states last year in Africa's most populous nation sparked bloody clashes between Christians and Muslims. Hundreds died.

Jos, with a government made up primarily of Christians and a heavy American missionary presence, has rejected the possibility of implementing Sharia.

Until now, the city, 125 miles from the capital, Abuja, had largely been spared religious and ethnic violence that has periodically wracked other parts of Nigeria.

Religious tensions in the city had been rising, however, following the recent appointment of a Muslim politician as chairman of a state poverty-alleviation committee.

On Saturday, President Olusegun Obasanjo called out the army to try to quell the bloodshed, and appealed to community and religious leaders of Jos to restore peace.

On Sunday, police sealed off the borders of Plateau state, blocking travel in and out.

Acting Gov. Michael Bomang sent out what was described as an "S.O.S." to dozens of cities and towns across the state, telling them to act to safeguard lives within their own communities.

There was no indication of any attacks on foreign church workers in Jos.

A hill station for Nigeria's one-time British rulers, Jos' mild climate attracted numbers of foreign missionaries from the colonial era on. American Methodists run a large boarding school in the city.