Newsbeat's guide to... Nigeria
The Foreign Secretary William Hague has said a British construction worker taken hostage in Nigeria last month is likely to have been killed.
Brendan Vaughan was one of seven foreigners kidnapped by Islamic extremists, who believe everything should be run according to strict religious rules.
The hostages - from Italy, Britain, Greece and Lebanon - were captured in a raid on a construction site in the northern state of Bauchi (see map below).
In an online statement posted on Saturday, the militant group Ansaru said it had killed the captives.
Who is the militant group Ansaru?
Ansaru is listed by the UK as a "terrorist organisation" aligned with al-Qaeda.
It is thought to be a breakaway part of the Boko Haram network - which has focused mainly on bombings and drive-by motorbike assassinations in north and central Nigeria since launching its insurgency in 2009.
Ansaru announced its formation in January 2012 and said it would target non-Muslims.
Its full Arabic name is Jama'atu Ansarul Muslimina Fi Bidalis Sudan, or vanguards for the protection of Muslims in black Africa.
They have used dynamite to get into heavily-fortified compounds to take foreigners hostage.
It said an attack last year was to avenge "transgressions" by European countries in Mali and Afghanistan, where Western forces are battling Islamist insurgents.
Why are western workers targeted?
Most kidnappings of westerners happen in the oil rich Niger Delta in the far south of the country, where expatriate oil workers are often ransomed.
Kidnappings have decreased since an amnesty for militants in 2009 but are on the increase again.
The former British colony is one of the world's largest oil producers but activists say few Nigerians have benefited from the oil wealth.
In retaliation they often steal oil and blow up pipelines which has led to the area becoming violent, corrupt and unstable.
There have also been regular oil spills.
Pirates operate in the area, with the Gulf of Guinea now in the same insurance risk category as Somalia.
Armed highway robberies are not uncommon and the families of Nigerian politicians and businessmen have also been targeted in the past.
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.
Nigeria's 160 million people are divided between numerous ethno-linguistic groups and also along religious lines. Broadly, the Hausa-Fulani people based in the north are mostly Muslims. The Yorubas of the south-west are divided between Muslims and Christians, while the Igbos of the south-east and neighbouring groups are mostly Christian or animist. The Middle Belt is home to hundreds of groups with different beliefs, and around Jos there are frequent clashes between Hausa-speaking Muslims and Christian members of the Berom community.
Southern residents tend to have better access to healthcare, as reflected by the greater uptake of vaccines for polio, tuberculosis, tetanus and diphtheria. Some northern groups have in the past boycotted immunisation programmes, saying they are a Western plot to make Muslim women infertile. This led to a recurrence of polio, but the vaccinations have now resumed.
Female literacy is seen as the key to raising living standards for the next generation. For example, a newborn child is far likelier to survive if its mother is well-educated. In Nigeria we see a stark contrast between the mainly Muslim north and the Christian and animist south. In some northern states less than 5% of women can read and write, whereas in some Igbo areas more than 90% are literate.
Nigeria is Africa's biggest oil producer and among the biggest in the world but most of its people subsist on less than $2 a day. The oil is produced in the south-east and some militant groups there want to keep a greater share of the wealth which comes from under their feet. Attacks by militants on oil installations led to a sharp fall in Nigeria's output during the last decade. But in 2010, a government amnesty led thousands of fighters to lay down their weapons.