Nigeria will lobby for its candidate to head the World Trade Organization (WTO), the country's foreign ministry said in reaction to her last-minute rejection by Washington that threw the regulator's leadership selection process into confusion.

The United States on Wednesday spurned Nigerian former finance minister Ngozi Okonjo-Iweala hours after a high-powered WTO panel recommended her to lead the global trade watchdog, teeing her up to become its first African and first woman head.

"Nigeria will continue to engage relevant stakeholders to ensure that the lofty aspiration of her candidate to lead the World Trade Organization is realised," the country's foreign ministry said in a statement on Thursday evening.

The ministry said the WTO's 164 member states were expected to adopt Okonjo-Iweala as the watchdog's director-general by consensus, but the United States was the sole country to oppose her, flouting the organisation's rules.

The US Trade Representative's office later released a statement officially backing the only other remaining candidate, South Korean trade minister Yoo Myung-hee, praising her as a successful trade negotiator with the skills needed to lead the trade body at a "very difficult time".

Next steps are uncertain, but a WTO spokesperson said there was likely to be "frenzied activity" before a November 9 meeting, less than a week after the US presidential election, to secure the required consensus from all 164 member states for Okonjo-Iweala.