Who are Nigeria's Boko Haram Islamists?
Nigeria's militant Islamist group Boko Haram - which has caused havoc in Africa's most populous country through a wave of bombings, assassinations and abductions - is fighting to overthrow the government and create an Islamic state.
Its followers are said to be influenced by the Koranic phrase which says: "Anyone who is not governed by what Allah has revealed is among the transgressors."
Boko Haram promotes a version of Islam which makes it "haram", or forbidden, for Muslims to take part in any political or social activity associated with Western society.
This includes voting in elections, wearing shirts and trousers or receiving a secular education.
Boko Haram regards the Nigerian state as being run by non-believers, even when the country had a Muslim president - and it has extended its military campaign by targeting neighbouring states.
The group's official name is Jama'atu Ahlis Sunna Lidda'awati wal-Jihad, which in Arabic means "People Committed to the Propagation of the Prophet's Teachings and Jihad".Resisting British rule
But residents in the north-eastern city of Maiduguri, where the group had its headquarters, dubbed it Boko Haram.
Loosely translated from the region's Hausa language, this means "Western education is forbidden".
Boko originally meant fake but came to signify Western education, while haram means forbidden.Boko Haram at a glance
- Founded in 2002
- Official Arabic name, Jama'atu Ahlis Sunna Lidda'awati wal-Jihad, means "People Committed to the Propagation of the Prophet's Teachings and Jihad"
- Initially focused on opposing Western education
- Launched military operations in 2009 to create Islamic state
- Designated a terrorist group by US in 2013
- Declared a caliphate in areas it controls in 2014
Since the Sokoto caliphate, which ruled parts of what is now northern Nigeria, Niger and southern Cameroon, fell under British control in 1903, there has been resistance among some of the area's Muslims to Western education.
They still refuse to send their children to government-run "Western schools", a problem compounded by the ruling elite which does not see education as a priority.
Against this background, the charismatic Muslim cleric, Mohammed Yusuf, formed Boko Haram in Maiduguri in 2002. He set up a religious complex, which included a mosque and an Islamic school.
Many poor Muslim families from across Nigeria, as well as neighbouring countries, enrolled their children at the school.
But Boko Haram was not only interested in education. Its political goal was to create an Islamic state, and the school became a recruiting ground for jihadis.
In 2009, Boko Haram carried out a spate of attacks on police stations and other government buildings in Maiduguri.
This led to shoot-outs on Maiduguri's streets. Hundreds of Boko Haram supporters were killed and thousands of residents fled the city.Facial marks
Nigeria's security forces eventually seized the group's headquarters, capturing its fighters and killing Mr Yusuf.
His body was shown on state television and the security forces declared Boko Haram finished.
But its fighters regrouped under a new leader, Abubakar Shekau, and have stepped up their insurgency.
In 2013, the US designated it a terrorist organisation, amid fears that it had developed links with other militant groups, such as al-Qaeda in the Islamic Maghreb, to wage a global jihad.
Boko Haram's trademark was originally the use of gunmen on motorbikes, killing police, politicians and anyone who criticises it, including clerics from other Muslim traditions and Christian preachers.
The group has also staged more audacious attacks in northern and central Nigeria, including bombing churches, bus ranks, bars, military barracks and even the police and UN headquarters in the capital, Abuja.
Amid growing concern about the escalating violence, President Goodluck Jonathan declared a state of emergency in May 2013 in the three northern states where Boko Haram is the strongest - Borno, Yobe and Adamawa.
It draws its fighters mainly from the Kanuri ethnic group, which is the largest in the three states. Most Kanuris have distinctive facial scars and when added to their heavy Hausa accents, they are easily identifiable to others Nigerians.
As a result, the militants operate mainly in the north-east, where the terrain is also familiar to them.Foreign links
The deployment of troops has driven many of them out of Maiduguri, their main urban base and they have now retreated to the vast Sambisa forest, along the border with Cameroon.
From there, the group's fighters have launched mass attacks on villages and towns in Nigeria, looting, killing and burning properties.
And it has switched tactics, often holding on to territory rather than retreating after an attack.
At the same time, Boko Haram has continued with its urban bombing campaign, and has also carried out cross-border raids into Cameroon.
In August 2014, Mr Shekau declared a caliphate in areas under Boko Haram's control - and pledged loyalty to Iraqi national Abu Bakr al-Baghdadi, the self-declared caliph (ruler) of Muslims worldwide.
"We are in an Islamic caliphate," said Mr Shekau, flanked by masked fighters and carrying a machine gun. "We have nothing to do with Nigeria. We don't believe in this name."
Boko Haram has also stepped up its campaign against Western education, which it believes corrupts the moral values of Muslims, especially girls, by attacking boarding schools.Chronic poverty
In April 2014, it drew international condemnation by abducting more than 200 schoolgirls from Chibok town in Borno state, saying it would treat them as slaves and marry them off - a reference to an ancient Islamic belief that women captured in conflict are part of the "war booty".
It had made a similar threat in May 2013, when it released a video, saying it had taken women and children - including teenage girls - hostage in response to the arrest of its members' wives and children. There was later a prison swap, with both sides releasing the women and children.
Analysts say northern Nigeria has a history of spawning militant Islamist groups, but Boko Haram has outlived them and has proved to be far more lethal, with a global jihadi agenda.
It has a fighting force of thousands of men and cells that specialise in bombings. Through its raids on military bases and banks, it has gained control of vast amounts of weapons and money.
The threat Boko Haram poses will disappear only if Nigeria's government manages to reduce the region's chronic poverty and builds an education system which gains the support of local Muslims, the analysts say.
Nigeria: A nation divided
Despite its vast resources, Nigeria ranks among the most unequal countries in the world, according to the UN. The poverty in the north is in stark contrast to the more developed southern states. While in the oil-rich south-east, the residents of Delta and Akwa Ibom complain that all the wealth they generate flows up the pipeline to Abuja and Lagos.