President Goodluck Jonathan said the violent Nigerian Islamist sect Boko Haram has supporters within his own government.
Here are some facts about Boko Haram.
THE GROUP * Boko Haram became active in about 2003 and is concentrated mainly in the northern Nigerian states of Yobe, Kano, Bauchi, Borno and Kaduna.
* Boko Haram, which in the Hausa language of northern Nigeria means "Western education is sinful", is loosely modelled on the Taliban movement in Afghanistan.
* The group considers all who do not follow its strict ideology as infidels, whether they be Christian or Muslim. It demands the adoption of sharia, Islamic law, in all of Nigeria.
* Boko Haram followers have prayed in separate mosques in cities including Maiduguri, Kano and Sokoto, and wear long beards and red or black headscarves.
* The group last week published an ultimatum that Christians had three days to get out of northern Nigeria. Since the ultimatum, attacks in northeastern Nigeria have left many dead with hundreds of Christians fleeing to the south. President Goodluck Jonathan declared a state of emergency in Nigeria on Dec. 31, in a bid to contain the violence.
SOME MAJOR ATTACKS: * In July 2009, Boko Haram staged attacks in the northeastern city of Bauchi after the arrest of some of its members, and clashed with police and the army in the northern city of Maiduguri. About 800 people were killed in five days of fighting in the two cities.
* Later that month, sect leader Mohammed Yusuf was captured by Nigerian security forces and shot dead in police detention some hours later.
* In early July 2010, Abubakar Shekau, a former deputy leader of the sect who was thought to have been killed by police in 2009, appeared in a video and claimed leadership of the group.
* In December 2010 the group said it was behind bombings in central Nigeria and attacks on churches in the northeast that led to the deaths of at least 86 people.
* On June 16, 2011, a car bomb tore through a car park outside Nigeria's police headquarters in Abuja, killing at least two people. Boko Haram claimed responsibility for the blast.
* On June 26, about 25 people were killed when several bombs exploded in the Dala ward of Maiduguri after suspected Boko Haram members threw bombs at a bar-cafe.
* On Aug. 25, Boko Haram members attacked Gombi police station in the northeast, killing four policemen and one soldier before driving to the First Bank and Union Bank where they killed seven staff and took an unspecified amount of money.
* On Aug. 26, a suicide bomber struck the U.N. building in Abuja. At least 23 people were killed and 76 wounded in the explosion. Boko Haram claimed responsibility on Aug. 29, demanding the release of prisoners and an end to a security crackdown aimed at preventing more bombings.
- The blast was the first known suicide bombing in Nigeria. It marked an escalation in the group's tactics and revealed an increase in the sophistication of explosives it uses.
- At least 65 people were killed in the city of Damaturu and the village of Potiskum on Nov. 4. The attacks, which also included a wave of bombings in Maiduguri, were some of the worst staged by the group.
- Boko Haram claimed responsibility for a series of bomb attacks across Nigeria on Christmas Day, including one at a church near Abuja that killed at least 37 people.