Nigerians are heading to the polls for the final round in a lengthy election process marred by violence.

Elections for Nigeria's 36 powerful governors have been delayed in two of the worst-hit states.
More bombs have exploded in the north-eastern city of Maiduguri, where at least three people have been killed
since Sunday. A Nigerian human rights group says more than 500 people died when clashes broke out after the presidential polls.
Violence erupted in the north after Goodluck Jonathan, a southern Christian, was declared the winner of the 16 April vote.
Churches were set alight and Muslims targeted in revenge attacks. Many Christians had to celebrate Easter in the military barracks where they had taken shelter from the riots.

Despite the violence, most observers said the elections had been among the best organised since the return of civilian rule in 1999. Poverty and religion 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.
The BBC's Mansur Liman in the capital, Abuja, says turnout is generally low in the northern states, with some people saying their votes do not count. He says security is tight.
The BBC's Tomi Oladipo says turnout also appears low in the biggest city, Lagos, possibly because of voter fatigue in the fourth week of elections. Some election officials, who are doing their national youth service have not turned up, after their colleagues were targeted during the previous violence.
The National Youth Corps workers do their service away from their home state and so are seen as vulnerable when violence breaks out.

"Very few corps members are left in [northern Gombe] state because we were not safe," one 25-year-old woman told the AP news agency.
It is unclear how much their absence will affect the elections.
European Union and US diplomats have issued a joint statement sharply criticising those behind violence and warning all of Nigeria's leaders to behave responsibly.
There are fears of intimidation in several areas, especially in the oil-producing Niger Delta.
The police commissioner in Maiduguri said no-one had been hurt by Tuesday's bombs. Previous bombings in the city were blamed on the Boko Haram Islamist group which has staged frequent attacks in recent months.
A total of 29 states out of 36 are holding their gubernatorial elections. Several delayed federal legislative
polls are also taking place.

Five governors only took office last year after winning their legal challenges against the 2007 elections and so new polls will not be held in those areas. The elections were postponed until Thursday in Kaduna and Bauchi following the clashes.

Correspondents say the governing People's Democratic Party faces a strong opposition challenge in several areas and is expected to lose some state governorships.

As in previous elections, voters are accredited from 0800 local time (0700 GMT), with actual voting due to start at 1230 local time.

The electoral marathon began with legislative polls on 9 April.
Mr Jonathan was appointed to the presidency last year upon the death of incumbent Umaru Yar'Adua, a northern Muslim 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.
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.

Source: BBC