A suicide bomb attack jolted a crowded bus station in the Nigerian capital Abuja Monday morning, killing at least 71 people and injuring 124 others.

No group has claimed responsibility for the attack yet, but Nigerian officials blamed the explosion on Boko Haram, a sect which has been responsible for major killings in the West African country since 2009.

The following are some key facts and a brief introduction of Boko Haram.

Proved to be the biggest security challenge in the West African country, Boko Haram seeks to enshrine the Islamic Sharia law into the constitution and declared war against Western education.

Founded in 1995, the group was originally named as Sahbaab, Muslim Youth Organization, with Maliam Lawal as the leader, who was replaced later by Mohammed Yusuf.

The group conducted its operations more or less peacefully during the following seven years, but things changed in 2009 when the Nigerian government launched an investigation into the group's activities following reports that its members were arming themselves.

Fights and clashes broke out between Boko Haram and Nigerian army afterward, with Boko Haram's leader Yusuf being killed in police custody.

After Yusuf's death, the group carried out its first attack in Borno, a northeastern state in Nigeria, in January 2011, killing four people. The violence has escalated both in its frequency and intensity.

- On Aug. 26, 2011, a car bomb targeting the United Nations headquarters in Abuja killed 26 people. Boko Haram claimed responsibility.

- On Dec. 25, 2011, a series of deadly explosions rocked Nigeria, leaving at least 39 dead and many others injured. Boko Haram claimed responsibility.

- On Nov. 13, 2013, the United States named Boko Haram and Ansaru as foreign terrorist organizations, slapping sanctions on them.

- On Dec. 2, 2013, an attack was launched against the Nigerian Air Force Base in Maiduguri, with some aircraft destroyed and two buildings razed. Boko Haram claimed responsibility.