Liam Fox, Britain’s former international trade secretary, has reached the last five in the race to be the next head of the World Trade Organization (WTO), the global customs and tariffs watchdog.

Fox, who was nominated by the British government for the post, will go into the second round of voting against nominees from Kenya, Nigeria, South Korea and Saudi Arabia.

WTO delegates are expected to whittle down the five candidates to two in October before choosing a winner the following month.

Boris Johnson tweeted his support, saying: “With a wealth of experience of institutional reform, and as a passionate advocate for international cooperation and free trade, the WTO would be in excellent hands under his leadership.”

The international trade secretary, Liz Truss, added: “Fantastic to see @LiamFox through to the 2nd round of the WTO director general race. His energetic campaign has gained the support of countries around the [world]. Liam is a fierce champion of free and fair trade and has the skills to move the @wto forward.”

A prominent Brexit supporter and longstanding supporter of free trade, Fox vowed to be a reformer should he win.

In a short film on his Twitter feed, he pledged to give the organisation more political impetus at a time when most international trade deals are held up by national concerns.

He said it was important to resolve disputes “not just in Geneva, but in national capitals as well”.

WTO regulators have faced cutbacks in funding by the US Trump administration, which has demanded it take a harder line against subsidised goods and services sold into the US from China, the EU and the UK.

However, revelations that Russian hackers were apparently able to obtain government documents marked “official sensitive [UK eyes only]” from Fox’s personal email last year are expected to damage his chances.

The former minister’s account is believed to have been accessed repeatedly and 451 pages of emails and policy documents were subsequently posted on Reddit, prompting questions as to whether the dossier had come directly from Fox’s personal email.

It is understood that Ngozi Okonjo-Iweala of Nigeria and Amina Mohamed of Kenya are the frontrunners as the WTO seeks to broaden its appeal and appoint its first woman and African to the top job.

Fox, who was a cabinet minister in Theresa May’s government between July 2016 and July 2019, and has been a Conservative MP since 1992, said he would make sure half of his senior advisers are women if he is elected.