Here are key facts on Nigeria's Boko Haram and Ansaru, which were designated as terror groups by the United States on Wednesday:
NAME: Roughly translates from the Hausa language spoken in northern Nigeria as "Western education is sin".
ORIGINS: An early version of the group formed in 2004 and is now believed to have a number of factions with differing aims, including some with political links and a hard-core Islamist cell.
AIMS: Originally claimed to be fighting for the creation of an Islamic state in northern Nigeria but different demands have since been issued, including prisoner releases.
LEADERSHIP: Boko Haram's first real leader was Mohammed Yusuf, who was killed after an uprising in 2009 that saw nearly a week of fighting and a military assault that killed some 800 and left the group's mosque and headquarters in the northeastern city of Maiduguri in ruins.
His former deputy, Abubakar Shekau, is currently believed to lead Boko Haram's main Islamist cell, which wants to be known as "People Committed to the Prophet's Teachings for Propagation and Jihad".
The United States has declared Shekau a "global terrorist" and offered up to $7 million (5.2 million euros) for information leading to his whereabouts.
Nigeria's military in August this year claimed Shekau was dead but he has been seen in videos released since.
AFFILIATES: Diplomats say Boko Haram members have sought training from Al-Qaeda's north African branch in northern Mali. Western countries are closely monitoring the group for signs of closer cooperation.
MODUS OPERANDI: Initially targeted local leaders and police in Nigeria's northeast but has since carried out suicide attacks against the United Nations, police and military as well as attacks on schools and higher education establishments.
Claimed responsibility earlier this year for kidnapping a French family, suggesting another shift in tactics. The family was later released in April.
Emergency rule imposed in Borno, Yobe and Adamawa states in May this year has pushed Boko Haram out of urban centres into the bush, where attacks have become more frequent.
NAME: Has identified itself as Jamaatu Ansarul Muslimina Fi Biladissudan, Arabic for "Vanguard for the Aid of Muslims in Black Africa".
ORIGINS: an offshoot of Boko Haram after the death of founder Mohammed Yusuf, with a more international agenda.
AIMS: Has mentioned France's intervention in Mali and European nations' "atrocities done to the religion of Allah" when claiming kidnappings and attacks.
But experts do not take such claims at face value and see the group more as a criminal gang with an Islamist strain.
LEADERSHIP: Unclear but some experts say Khalid al-Barnawi -- one of three Nigerian extremists labelled a "global terrorist" by the United States last year -- is its leader.
AFFILIATES: The group is believed to have links of some kind with Al-Qaeda in the Islamic Maghreb (AQIM), Al-Qaeda's north African wing.
The US State Department described Barnawi as tied to Boko Haram and with "close links" to AQIM. Its kidnappings would seem to mimic those claimed by AQIM in other countries.
MODUS OPERANDI: Has been linked to at least three hostage-takings of foreigners since 2011, including a Briton and an Italian working for a construction firm who were killed in 2012 in a botched rescue operation.
Ansaru claimed responsibility for the December 2012 kidnapping of a French engineer in Katsina state, bordering Niger, and killing seven foreign workers earlier this year.
It also claimed a January 19 attack in central Nigeria that killed two soldiers due to be deployed to Mali.