Updated

More than 1,500 people have been killed so far this year in attacks blamed on the Nigerian radical group Boko Haram, whose name means "Western education is forbidden" in the local Hausa language. The terrorist network's mission is to force an Islamic state on Nigeria, Africa's most populous nation of some 170 million people divided almost equally between Muslims living mainly in the north and Christians in the south.

Nigeria's Islamic extremist insurgency grew out of a 2009 riot led by Boko Haram members in Maiduguri, once home to the group's main mosque, that ended in a security forces' attack that killed some 700 people. The group's leader was shot and killed in police custody, fueling dissent that broke into the open in 2010 with the targeted killings of government officials, security agents and religious leaders who spoke out against the sect.

The killings gradually morphed into the large-scale indiscriminate attacks plaguing Nigeria today, on schools, villages, market places, military barracks, churches and mosques that have led to the deaths of thousands. Boko Haram's message — that Shariah law will end Nigeria's endemic corruption and poverty affecting 70 percent of the nation — appeals to some of the millions of unemployed and ill-educated Muslim youths living in the most impoverished part of the country.

The U.S. in 2013 declared Boko Haram a foreign terrorist organization and put a ransom of $7 million on the head of leader Abubakar Shekau.

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Here is a look at recent major attacks attributed to Boko Haram, with some of the highest death tolls:

__April 14, 2014: A massive explosion believed caused by a bomb buried in the ground rips through a bus station during the morning rush hour in Nigeria's capital, killing at least 71 people and wounding 124.

__March 14, 2014: Boko Haram launches an assault on the main Giwa Barracks in Maiduguri and claims to have freed 2,000 detainees held there. The battle that ensues kills about 425 people, mainly detainees that included civilians, according to hospital workers who said they were forced to hold a mass burial because the morgue could not hold all the bodies.

__Feb. 25, 2014: Islamic extremists kill at least 59 students at a boarding school in Yobe state, locking some into a dormitory and burning them alive. Survivors say the attackers first went to female dormitories and told the young women to go home, get married and abandon the Western education they said is anathema to Islam.

__Feb. 19, 2014: Islamic extremists attack agricultural and commercial center Bama town, killing at least 115 people, razing more than 1,500 homes and destroying some 400 vehicles. The attack comes the same day the leader of the terrorist network warns leading Nigerian Muslim political, religious and traditional leaders that his fighters will target them for pursuing democracy and Western-style education.

__Feb. 16, 2014: Chanting "Allah is great," Islamic militants gun down dozens of villagers and slit the throats of others, killing more than 50 people in Izghe village in Borno state in an area of northeast Nigerian area where the military has been bombing extremists out of forest hideouts. Attacks, including this one, over the weekend on eight villages in Borno and Adamawa states leave more than 150 people dead.

__Jan. 26, 2014: Extremists blow up the main market with homemade bombs, shoot at people and then set huts on fire in Kawuri village, killing at least 85 people.

— Jan. 20, 2012: Boko Haram claims responsibility for a series of coordinated bombings and gun battles around the city of Kano that kill at least 185 people.

— Dec. 25, 2011: Boko Haram claims responsibility for a Christmas Day attack on a Catholic church in Madalla near Nigeria's capital and two churches elsewhere that kill at least 42 people.

— Nov. 4, 2011: Boko Haram members bomb government buildings and shoot their way through the city of Damaturu, killing more than 100 people, while bombs and a suicide attack in Maiduguri leave 4 dead.

— Dec. 24, 2010: A series of bombs allegedly planted by the group explode in the central Nigerian city of Jos, killing as many as 80 people.