Nigeria's radical Islamist sect Boko Haram is suspected to be behind almost daily attacks in the remote northeast and claimed a series of bomb blasts further afield last month. Following are questions and answers on who the group are, what they want, and whether their ideology is widely followed.
WHAT IS BOKO HARAM?
Based in Maiduguri, capital of the northeastern state of Borno, it was initially led by self-proclaimed Islamic scholar, Mohammed Yusuf, who was radically opposed to Western education and wanted strict sharia Islamic law adopted across Nigeria.
Sometimes referred to as the "Nigerian Taliban", the group's name means "Western education is sinful" in the Hausa language spoken across northern Nigeria.
Boko Haram followers pray in separate mosques in cities including Maiduguri, Kano and Sokoto, and wear long beards and red or black headscarves.
They believe their wives should not be seen by any men other than themselves and are not supposed to use Western-made goods.
Anybody who does not follow their strict ideology - whether Christian or Muslim - is considered an infidel.
It is unclear how many followers the sect has but poverty, unemployment and a lack of education in the far northeast have enabled its leaders to build a cult-like following which is as much violently anti-establishment as fervently religious.
WHAT ARE ITS AIMS?
A detained leader of an uprising in 2003, in which around 20 people were killed, said the group was fighting to overthrow the Nigerian government because it had "sold out to the West".
Boko Haram rose to prominence in 2009 when it launched attacks on government buildings, leading to clashes with the police and army in which up to 800 people were killed.
Yusuf was captured during the uprising and shot dead in police custody. His mosque was destroyed by tanks, in what the security services said was a decisive victory against the sect.
But small-scale guerrilla attacks continued, including drive-by shootings from motorbikes and home-made bomb attacks.
The killings intensified in the second half of 2010, with the targets mostly soldiers, policemen, prison warders and politicians as well as religious and traditional rulers opposed to the group's ideology.
It has been blamed for killing of Imams and senior Islamic figures, including the brother of the Shehu of Borno, the leader of one of West Africa's oldest Islamic communities, last month.
It claimed responsibility for Christmas Eve bombings in the central city of Jos and also for co-ordinated bomb attacks in three towns after President Goodluck Jonathan was inaugurated on May 29, 2011.
IS THERE A HISTORY OF SECTARIAN VIOLENCE IN NIGERIA?
Africa's most populous nation is roughly equally divided between Christians and Muslims and more than 200 ethnic groups generally live peacefully side by side, although civil war left one million dead between 1967 and 1970.
The stricter enforcement of sharia in 12 of Nigeria's 36 states in 2000 alienated sizeable Christian minorities in the north and sparked clashes which killed thousands.
In 2002 at least 215 people died in rioting in the northern city of Kaduna following a newspaper article suggesting the Prophet Mohammad would probably have married one of the beauty queens at a Miss World contest being held in Abuja.
A Muslim protest against Danish cartoons of the Prophet Mohammad in the northern city of Maiduguri ran out of control in 2006, sparking a week of rioting which killed at least 157.
Human rights groups said rioting in parts of the mostly Muslim north killed as many as 800 people after President Jonathan, a Christian from the south, was named winner of April, 2011 elections beating northern Muslim rival Muhammadu Buhari.
The worst of the violence took place on the edge of a region known as the Middle Belt, where there have been frequent ethnic and religious clashes for more than a decade, mostly rooted in rivalry over fertile farmland and economic power.
DOES RADICAL ISLAM HAVE A FOOTHOLD IN WEST AFRICA?
West Africa has a strong tradition of moderate Sufi Islam whose brotherhoods are renowned for their tolerance, particularly in the Sahel - the southern fringe of the Sahara desert stretching across the northern edge of Nigeria.
Boko Haram's ideology is widely dismissed by the most of the country's Muslim leaders and believers.
Salafist insurgents from Algeria, Tablighi clerics from Pakistan and Wahabist missionaries from Saudi Arabia - all seen as potential threats by Western intelligence services - have tried to gain a foothold in West Africa in recent years.
By and large they have failed.
But the main militant threat in the Sahara is seen as al Qaeda in the Islamic Maghreb (AQIM), which grew out of Algeria's civil war in the 1990s and was formerly known as the Salafist Group for Preaching and Combat (GSPC).
Nigeria arrested a group of Islamists with suspected links to al Qaeda in 2007 and some Western diplomats have expressed concerns that - with its huge population, widespread poverty and strategic importance as an oil supplier to the West and to China - it could become a target for radical Islamist groups.
Intelligence sources say there is evidence that some members of Boko Haram have trained over the border in Niger where AQIM is known to have a presence.
