Nigerian states of Kaduna and Bauchi vote after riots
There is tight security in two northern Nigerian states hit by rioting last week as counting began after polls delayed because of the unrest.
Bauchi and Kaduna witnessed the worst of the violence in which some 500 people died after the results of the presidential poll were announced.
This week's elections for governors took place in other states on Tuesday.
The governing People's Democratic Party (PDP) has unexpectedly lost two states in the south-west of the country.
Ogun state - home to former President Olusegun Obasanjo - and Oyo were both won by the opposition Action Congress of Nigeria, which now controls almost the whole region.
The PDP also lost two other states but gained Kano, the most populous state in the north.
Election officials say the result in the south-eastern Imo state was too close to call.
Governors enjoy wide powers in Nigeria and some, especially in oil-producing areas, control bigger budgets than those of national governments in some neighbouring West African countries.
Turnout in Bauchi and Kaduna appears to have been low.
"People are still scared because of last week's mayhem," Solomon Patrick, a 41-year-old civil servant told the AFP news agency at a polling place in Bauchi city.
Herds of cattle roamed the streets of Kaduna city on Thursday morning, with few people lining up at polling stations, Reuters news agency reported.
It says there were more security agents than voters at the polling station where Vice-President Namadi Sambo voted and many polling stations closed early because of a lack of voters.
President Goodluck Jonathan, a southern Christian, was declared the winner of presidential elections but northern supporters of his closest challenger former military ruler Muhammadu Buhari cried foul and took to the streets.
Mr Jonathan was appointed to the presidency last year upon the death of incumbent Umaru Yar'Adua, a northerner whom he had served as vice-president.
Many in the north felt the next president should have been from their region, as Mr Yar'Adua died before he could finish his term.
Gen Buhari won most of the mainly Muslim northern states but nationwide only gained half as many votes as President Jonathan.
Analysts say the violence has more to do with poverty and economic marginalisation in the north than religion.
The north and south also have cultural, ethnic and linguistic differences.
Despite the violence, most observers said the elections had been among the best organised since the return of civilian rule in 1999.
Nigeria's electoral marathon began with legislative polls on 9 April, in which the PDP lost some ground but retained its majority.
To win at the first round, a candidate not only needs the majority of votes cast, but at least 25% of the vote in two-thirds of Nigeria's 36 states. Goodluck Jonathan, of the PDP, reached that threshold in 31 states; runner-up Muhammadu Buhari of the CPC only did so in 16 states.
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.
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.
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.