Saying that global trade is passing through "challenging times", Union Commerce and Industry Minister Suresh Prabhu on Saturday said the existence of World Trade Organisation (WTO) was under threat.According to him, WTO is "a must" and in its absence, there will be chaos in the global trade."Today, it is the most challenging time for global trade... we never had such a challenging time. For the first time, the existence of WTO is under threat. People are questioning the accepted trading norms," he said at an event organised by Federation of Indian Export Organisations here.Citing an example of "letter of credit", a prerequisite for exports to happen, Prabhu said fundamentals of global trade are "under scrutiny"."If you don't have WTO, not only India, every country will have problem. We strongly feel WTO is a must because it guarantees certain rules and regulations to run global trade. There will be chaos if you don't have WTO."Prabhu said the country was trying to make the global organisation strong."We are not only talking of reform of WTO and working on how revitalise it. I personally work with important ministers of the world and am trying to find out (the way forward)... improving WTO is one thing and discarding it is a different thing," he added.