More than 1,000 Nigerians have fled to neighboring Niger after six people were killed in an attack on their village blamed on Islamist group Boko Haram, the United Nations said Thursday.

The 1,042 refugees crossed the northern border into the Niger region of Diffa after the November 30 attack, and have been taken in by families in two villages near the regional capital, the U.N. Office for the Coordination of Humanitarian Affairs (OCHA) said in a bulletin.

Two explosions Monday rocked two different Nigerian cities repeatedly hit by attacks blamed on Islamist extremist group Boko Haram, wounding at least four people, police and residents said.

The explosions occurred in Kano, the largest city in northern Nigeria, and Maiduguri, the northeastern city at the heart of Boko Haram's insurgency.

Suspected members of the Islamist extremist group Boko Haram set fire to churches and border posts in northeastern Nigeria on Sunday, residents said, in an attack that left at least two policemen dead.

Around 50 gunmen in cars and on motorcycles carried out the attacks on three churches and border posts with neighboring Cameroon, opening fire on police and chanting Allahu Akbar (God is Greatest), residents said.

Gunmen said to be dressed as soldiers opened fire on a central Nigeria pub, killing 10 people in a region hit by waves of clashes between Christian and Muslim ethnic groups, authorities said Tuesday.

The incident occurred in the Barkin Ladi area of Plateau state late Monday and saw gunmen storm the pub then open fire indiscriminately on customers, according to a military spokesman who denied soldiers were involved.

Gunmen have kidnapped two foreign workers from a construction site in Nigeria's oil-rich Niger Delta region, police said Tuesday, while local media said the victims were Lebanese.

The two "were taken from a construction site in the creeks of Delta State yesterday (Monday)," state police spokesman Charles Muka told Agence France Presse.

Gunmen attacked a Nigerian police unit believed to be holding suspected Islamist extremists in the capital Abuja on Monday, killing two officers and leading to the escape of 30 detainees.

Authorities however claimed to have re-arrested 25 of the 30 escapees and said no one being held on "terror-related charges" was freed.

Gunmen sought to attack a special police unit in the Nigerian capital Abuja on Monday as a police spokesman claimed the assailants were "repelled".

"I can confirm that there was an attempted attack on the (special anti-robbery squad) this morning which was repelled," spokesman Frank Mba said, adding that the attackers were "suspected gunmen".

A suicide bomber rammed a bus into a church at a military barracks in restive northern Nigeria on Sunday and another detonated his explosives-packed car minutes later, killing 11 people and wounding dozens more.

The first bomb attack struck minutes after Sunday mass in the town of Jaji, the latest such attack against Christians in the west African nation where the Islamist extremist group Boko Haram has waged a deadly campaign.

Nigeria's military on Friday offered hundreds of thousands of dollars in rewards for information leading to the capture of leaders of Islamist extremist group Boko Haram.

A statement listed 19 alleged senior members of the extremist group blamed for hundreds of deaths in connection with its insurgency in northern and central Nigeria.

A mispronunciation taken to be blasphemous in Nigeria's north sparked a riot by Muslim youths Thursday, leaving four people dead as well as a church and shops burnt, police and residents said.

"What happened in (the town of) Bichi was misinformation," Kano state police chief Ibrahim Idris told reporters. "Rumors went round that someone blasphemed the Prophet and there was a breakdown of law and order."