A fight over a game of billiards disintegrated into religious violence in northern Nigeria, leaving at least four people dead among the smoldering ruins of churches and mosques, authorities said Thursday.

The attack in the town of Tafawa Balewa in Bauchi state came the same day police said members of a radical Muslim sect killed a police officer guarding a voter registration site in northeast Nigeria. The attack showed the continuing ability of members of the Boko Haram sect to kill at will despite a military and police crackdown, leaving a state police commissioner to admit he cannot guarantee the safety of election officials.

The violence also comes ahead of April elections that many worry could ignite simmering ethnic and religious tensions in a country that became a democracy only a decade ago. Those tensions have seen more than 200 people die in the last month's time around the central Nigerian city of Jos, a flash point of violence between Nigeria's two dominant faiths, Human Rights Watch said Thursday.

In Tafawa Balewa, the home of Nigeria's assassinated first prime minister Abubakar Tafawa Balewa, the violence started Wednesday night, said Bauchi state police Mohammed AbdulKadir Indabawa. Indabawa said a group of youths playing billiards got into an argument, which sparked violence in a town familiar to riots between Christians and Muslims.

Paramilitary police patrolled the city's streets Thursday as mosques, churches and homes sat destroyed, Indabawa said. The commissioner said he believed soldiers also would join the security crackdown.

"We've mounted road blocks at areas leading to the town to avoid a spillover of the crisis to other areas," Indabawa said.

Meanwhile, Borno state police commissioner Ibrahim Abubakar told The Associated Press on Thursday that an officer in Maiduguri died Wednesday night after being shot while guarding a primary school holding registration equipment. Abubakar said another officer was wounded in an attack by gunmen riding motorcycles, an assault that follows the pattern of others allegedly committed by the Boko Haram sect in the arid, dusty city.

Nigeria is in the midst of an effort to register an estimated 70 million eligible voters before its elections. Abubakar said the attack Wednesday night showed police were unable to defend the university graduates staffing the registration effort.

"Voters' registration materials should be kept at the nearest police stations," the commissioner said.

Boko Haram, which means "Western education is sacrilege" in the local Hausa language, has attacked churches and engineered a massive prison break in recent months.

The violence in central and northern Nigeria comes as President Goodluck Jonathan, a Christian who took over Africa's most populous nation after the death of its elected Muslim leader, seeks the presidency. Some believe a northern candidate should stand in Jonathan's place to appease an unwritten power-sharing agreement in the oil-rich nation's ruling party.

While Jonathan overwhelming won the party's recent primary, some fear more violence cutting across the country's ethnic, religious and political lines will come as the election draws near.

Since Dec. 24, the central Nigerian city of Jos and its surrounding villages has seen more than 200 people killed in retaliatory violence, Human Rights Watch said. Bombs struck around the city Christmas Eve, while others have been shot, hacked to death by machetes or had been "disappeared," the rights group said.

At least 1,000 people died around the city in 2010 in violence that cut across religious lines, but often found its root in political, economic and ethnic strife.

"This terrible cycle of violence and impunity needs to stop," Human Rights Watch researcher Corinne Dufka said in a statement. "Both the state and federal governments have shown a disturbing lack of urgency in addressing the violence and tackling the underlying causes of these deadly outbreaks."


Njadvara Musa reported from Maiduguri, Nigeria. Jon Gambrell in Lagos, Nigeria contributed to this report.

(This version corrects spelling of Bauchi state police commissioner.)