Lagos, Nigeria (CNN) -- A gubernatorial candidate in the northern Nigerian state of Borno was assassinated, and five police officers and the governor's brother were also killed in a gun attack outside a mosque Friday, said Borno state police commissioner Abubakar Mohammed.
"This was not Boko Haram. This was political assassination," Mohammed said. Boko Haram is an Islamic fundamentalist group in the region.
Three men on motorbikes gunned down leading Borno state gubernatorial candidate Modu Fannami Gubio of the All Nigeria People's Party, Mohammed said.
The violence occurred in Maiduguri, the capital of Borno, said Red Cross Borno secretary Mohammed Barma.
Also killed were the Borno governor's younger brother, Goni Sherrif, and five plainclothes police officers, commissioner Mohammed said. The assassination came after afternoon prayers, he said.
The current governor, who has reached his two-term limit, is a member of the same party to which Gubio belonged.
The violence occurred in the lead-up to April's elections, in which Nigerians will also elect a new president.
It also comes in a month marked by deadly sectarian violence in central Nigeria in which more than 200 persons have been killed, a human rights monitoring group said Thursday.
Nigeria's Independent National Electoral Commission has extended the registration period by a week after a very widely and publicly criticized start. Voters now have until February 5 to register, instead of January 30, said commission secretary Alhaji Abdullahi Kaugama in a statement.
The INEC chairman told the Senate on Wednesday that an extra week will cost more than $43 million.
The extension is designed to yield a more complete roll of registered voters. The 2007 vote were considered one of Nigeria's most corrupt elections.
In this month's bloodshed, the victims, including children, have been hacked to death, burned alive, dragged off buses and have "disappeared," Human Rights Watch said.
The group appealed to the Nigerian government to "act swiftly to protect civilians of all ethnicities at risk of further attacks or reprisal killings." It also urged the government to allow Francis Deng, the United Nations secretary-general's special adviser on the prevention of genocide, to visit central Plateau state.
"This terrible cycle of violence and impunity needs to stop," Corinne Dufka, the group's senior West Africa researcher, 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."
The wave of violence began with Christmas Eve bomb blasts in two Christian communities in Jos, the state capital that lies on a faith-based fault line between Muslim-dominated northern Nigeria and the mainly Christian south. At least 31 people died in those attacks.
Since then, dozens of Muslims and Christians have been targeted and killed based simply on their ethnic or religious identity, Human Rights Watch said. It follows a year of bloodshed in 2010 that left at least 1,000 people dead in Plateau state.
Deng submitted a request to travel to Jos in October but Human Rights Watch said the Nigerian government has not formally replied or authorized the mission.
Earlier this month, eight Muslim youths heading to a wedding were attacked after they took a wrong turn and ended up in a Christian village. Witnesses told Human Rights Watch that the Nigerian army exhumed five bodies from shallow graves near the village and returned them to their families. The three others remain missing.
In reprisal, Muslim youths in Jos attacked Christians the next day. Witnesses told Human Rights Watch that the victims were hacked to death with machetes and cutlasses or burned alive by the mob.
Later that day, at least 14 more Muslims were killed by mobs in Christian neighborhoods in the Jos area.
Witnesses told the rights group that Muslims and Christians were separated on buses, dragged off and hacked to death. Others spoke of people burned alive in their houses.
In Nigeria, Africa's most populous nation, more than 13,500 people have died in religious or ethnic clashes since the end of military rule in 1999, Human Rights Watch said in a report last year. The group charges the government exploits the violence for political gain.
CNN's Christian Purefoy contributed to this report.