MAIDUGURI, Nigeria (AP) — The woman who led the global campaign to free Nigerian schoolgirls kidnapped by Boko Haram extremists is dropping out of the race for Nigeria's presidency.

Oby Ezekwesili is the most prominent woman to seek the presidency in Nigeria, where politics, as in many African nations, have long been dominated by men.

She said in a series of tweets Thursday that she plans to focus on building a "strong and viable" opposition coalition to challenge Nigeria's two main political parties before the Feb. 16 vote.

She criticized what she called "the mess that has now become the political class."

President Muhammadu Buhari seeks a second term in the election and the top challenger is veteran politician Atiku Abubakar.

The winner will lead Africa's biggest crude oil producer and most populous country.