The leader of Nigeria's Christians called Tuesday on the United States to declare the Islamist group Boko Haram to be terrorists, but a U.S. official said it was more important to address social inequalities.

In an unusually blunt appeal by a foreigner before the U.S. Congress, the head of the main Christian body in religiously divided Nigeria said that a decision to blacklist three Boko Haram leaders as terrorists did not go far enough.

Nigeria's Boko Haram Islamists on Tuesday claimed a weekend attack at a graveyard in central Plateau state that left at least 22 people dead, including two prominent politicians.

Police and officials have blamed nomadic herdsmen for the raid, but in a statement issued from purported spokesman Abul Qaqa, Boko Haram said it "wants to inform of its delight over the success of the attacks we launched... in Plateau state."

Gunmen killed several people in an attack on two Christian villages in central Nigeria's Plateau State early Saturday, officials said.

Although police and army spokesman could not give an exact toll, one politician said at least 23 people had been killed and blamed Muslim herdsmen for the attacks.

Nigerian troops killed one person during a raid on a suspected hideout of Islamist group Boko Haram in the restive northeastern city of Damaturu, a hospital source and residents said Saturday.

Explosions and gunfire rocked the city, the capital of Yobe State on Friday, in the latest clampdown by the military Joint Task Force (JTF) on members of the sect, they said.

Gunfire and explosions rocked a northeastern Nigerian city as security forces launched a pre-emptive offensive against Boko Haram Islamists, leaving three dead, police said Sunday.

The offensive on Saturday followed intelligence that the extremist group planned to attack the restive city of Damaturu again, said the deputy police spokesman of Yobe state.

Nigeria's military on Saturday said it had arrested the leader of a gang responsible for a series of attacks on oil installations in the Niger Delta region.

Seifa Gbereke, known locally as "General Cairo," is also suspected of stealing crude from pipelines, a widening practice that costs Africa's largest producer roughly $5 billion a year, according to some estimates.

Attackers with guns and explosives raided a jail in a restive Nigerian city on Sunday, leaving four prison guards dead and freeing 40 inmates, authorities said.

An explosion went off outside a nightclub in the Nigerian capital Abuja, breaking windows and damaging cars, but no casualties were reported, the country's emergency agency said on Saturday.

"No human casualty," Yushau Shuaib, spokesman for the National Emergency Management Agency, said of the blast late Friday. "The explosives were suspected to have been planted on a tree opposite Kryxtal Lounge."

Nigerian President Goodluck Jonathan fired his national security adviser and defense minister on Friday, his spokesman said, as fears mounted over spiraling unrest in the country's north.

Nigeria has faced a deadly insurgency from Islamist group Boko Haram, who have launched a bloody series of bomb and gun attacks.

An Islamist insurgency that has increasingly targeted churches has sparked fears of wider unrest in Nigeria after anger boiled over at the weekend, resulting in deadly riots by Christian mobs.

Christian leaders and others in Africa's most populous nation have warned in recent days that the government's failure to stop Islamist group Boko Haram could lead to more cases of residents taking the law into their own hands.