Reuters looks at Boko Haram and some of the major attacks it has carried out especially against Christians and places of worship:

* Boko Haram became active in 2003 and carried out its first attack in 2004. It has its heartland in the far northeastern corner of Nigeria around Maiduguri. In the Hausa language, Boko Haram means "Western education is sinful." It is loosely modelled on the Afghan Taliban and its followers wear long beards and red or black headscarves.

* Boko Haram is fighting to impose Islamic, or sharia, law on Nigeria, whose population of 160 million people is split evenly between Christians and Muslims. At least 2,800 people have died in fighting in the largely Muslim north since the sect launched an uprising against the government in 2009, watchdog group Human Rights Watch says. Its most lethal attack killed at least 186 people in Kano in January 2012 in coordinated bombings and shootings.

* Boko Haram has repeatedly struck churches during services, carrying out attacks at Christmas and Easter which have killed scores of people. An attack on St. Theresa's Catholic church in Madalla on Abuja's outskirts during a packed Christmas mass in 2011, was the deadliest of a series of Christmas attacks on Nigerian churches and other targets by the sect. At least 37 people were killed. Last Easter Sunday an attempted bombing at a church compound in northern Kaduna during a service went wrong and the bomb exploded by a large group of motorbike taxi riders, killing at least 36 people.

* Other major attacks - Gunmen killed at least 19 people in two attacks on Christian worshippers in the Nigerian city of Kano and in the northeastern town of Maiduguri on April 29, 2012. In June, three gunmen sprayed bullets at the congregation of a church in Biu Town, in northeastern Borno state. In Jos, suicide bomber drives car to the entrance of the Christ Chosen Church and blew it up. Boko Haram claimed both attacks.

* A bomb attack in a church in Kaduna state in June triggered a week of tit-for-tat violence that killed at least 90 people. In October a suicide bomber drove a jeep full of explosives into a Catholic church during morning mass, killing eight and wounding more than 100. There was no claim of responsibility. The most recent attack took place last month when suicide bombs struck the St. Andrew Military Protestant Church at the Jaji barracks in Kaduna state killing 11 people and wounding 30. Sources: Reuters/Janes World Insurgency and Terrorism, 2012 (For full Reuters Africa coverage and to have your say on the top issues