Nigerian Finance Minister Ngozi Okonjo-Iweala and former Colombian Finance Minister Jose Antonio Ocampo are set to be nominated to lead the World Bank, sources with knowledge of emerging market efforts to find candidates said on Tuesday.

The candidacies of Okonjo-Iweala and Ocampo, who have credentials as both economists and diplomats, pose a challenge to the United States, whose hold on the top post has never been contested.

Washington has held the presidency since the Bank's founding after World War Two. It has yet to publicly identify a nominee to succeed Robert Zoellick, who plans to step down when his term expires at the end of June. The deadline for submitting nominations is Friday.

All of the World Bank's 187 members nations have committed to a merit-based process to select Zoellick's successor.

Okonjo-Iweala, who left the World Bank as managing director last year to become Nigeria's finance minister, and Ocampo, a former U.N. under-secretary for economic and social affairs, will join American economist Jeffrey Sachs, who has the backing of a handful of small countries, on the nomination list.

Nominations will be submitted to the 25-member World Bank board, which has said it will decide on the next president within the next month.

Two sources said Okonjo-Iweala's candidacy had the blessing of Nigerian President Goodluck Jonathan. – Reuters