LAGOS, Feb 6 (Reuters) - The governor of Lagos said the population of the teeming city was 17.5 million and rejected a national census that gave Lagos half that number in a row that underscores Nigeria's ethnic and political tensions.
Africa's most populous nation attempted its first census in 15 years in March 2006 but since the results came out last month many in the predominantly Christian south have complained they were short-changed in favour of the mainly Muslim north.
Census figures affect the sharing of oil revenues and political representation among Nigeria's 36 states and 300 ethnic groups. Previous counts were discredited after disputes among the three main groups, the Fulani, Yoruba and Ibo.
Lagos, a sprawling port city where millions live in overcrowded slums, is in the southwestern Yoruba heartland. Nigerians from all over the country flock to Lagos in the hope of doing business in a city famed for its entrepreneurship.
The 2006 census found that Nigeria had 140 million people of whom a little over half were in the north. Results said northern Kano state was the most populous with 9.4 million while Lagos was in second place with 9 million.
But the Lagos state government conducted its own headcount in parallel with the national one, and Governor Ahmed Bola Tinubu has said the result was 17.5 million and the state would challenge the 9 million figure in parliament and in the courts. Lagos state is almost entirely made up of the city of Lagos.
"The figure is totally rejected ... The database is faulty. It has to be discarded," Tinubu was quoted as saying in Tuesday's Guardian newspaper.
Nigeria's complex political system has been delicately balanced for decades on the assumption that the north has a numerical advantage and the 2006 census upheld that status quo.
Elections are coming up in April and any challenge to the old north-south balance could have caused violence in the north, which expects the presidency to go to a Muslim northerner after eight years in the hands of a Christian Yoruba.
But the national census figures have been widely derided in the south, where almost everyone is convinced that Lagos is the biggest city in Nigeria and in the whole of sub-Saharan Africa.
In the north, people argue that while Kano city may be smaller than Lagos, its rural hinterland is densely populated. They also say northerners have more children and therefore the population grows faster.
Nigeria is a complex ethnic mosaic, marked by rivalries between the three biggest groups and perpetual fears among minority groups that one of the big three would gain domination over the country.
In particular, there is a widespread fear in the south of northern domination. Most of the army dictators who ruled Nigeria for almost three decades were from the north.