YAOUNDE, March 26 (Reuters) - Trade ministers will meet in Cameroon on Thursday for crucial discussions on reforming the World Trade Organization, as some diplomats and trade officials warn that without an agreement, countries may set trade rules outside the organisation.

The four-day gathering in Yaounde comes amid concerns over the impact of the U.S.-Israeli war on Iran on global trade, following a year of tariff turmoil triggered by U.S. President Donald Trump's weaponization of trade measures.

"From a business perspective this could yet become the worst industrial crisis in living memory," said John Denton, secretary-general of the International Chamber of Commerce, warning of the impact from energy price spikes caused by the war, and subsequent food security risks in Africa due to fertilizer supply disruptions.

After years of stalled multilateral deals and a six-year paralysis of the WTO's dispute settlement system, ministers arrive in Yaounde without a clear reform roadmap amid deep divisions.

The U.S. supports reforms but is resisting a detailed work plan, while the EU, Britain, and China back one, internal reform documents seen by Reuters show. WTO Director-General Ngozi Okonjo-Iweala said she expected the talks to be difficult.

If ministers leave empty-handed, diplomats and officials warned it could push members to pursue other options for trade rulemaking.

"If we don't achieve anything concrete, the WTO will lose its attractiveness and relevancy," Swiss Ambassador Erwin Bollinger said ahead of the talks. 

UK trade minister Chris Bryant warned of potential fragmentation if no deal is reached. 

"My anxiety is if we ministers don't get this week right, you might see a disorderly collapse of the WTO and some people writing a new rule book," Bryant said.

Talks are expected to be tense, with the U.S. and India set for a showdown over the extension of a moratorium on customs duties for digital downloads. 

U.S. Trade Representative Jamieson Greer, in a draft statement seen in advance by Reuters, is expected to tell members the U.S. is "not interested" in a temporary extension, only a permanent extension. India, however, is likely to maintain its opposition, an official said, while some other countries seek a two-year extension. 

South Korea Trade Minister Yeo Han-Koo said failure to extend the moratorium would be a "big blow" to the WTO and the global economy.

Semiconductor powerhouse Taiwan will not attend after host country Cameroon described it as a province of China.