GENEVA - The head of the United Nations said on Wednesday that the global trade system was facing major challenges due to tariffs, with developing countries worst affected.

"The rules-based trading system is at risk of derailment," UN Secretary-General Antonio Guterres told delegates at the UN Trade and Development conference in Geneva on Wednesday, pointing to concerns about trade wars and rising trade barriers.

US President Donald Trump's tariff decisions since he took office in January have shocked financial markets and sent a wave of uncertainty through the global economy.

On August 7, Trump imposed higher tariffs on imports from dozens of countries, leaving major trade partners like Switzerland, Brazil and India scrambling for a better deal.

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"Supply chains are in turmoil, and trade barriers are rising, with some least developed countries facing extortionate tariffs of 40 percent despite representing barely 1 percent of global trade flows," Guterres said.

While the EU has struck a deal setting duties at 15 percent on most goods it exports to the United States, they are often much higher on so-called least developed countries. Laos, for example, faces tariffs at 40 percent.

Earlier this month the World Trade Organization sharply lowered its 2026 forecast for global merchandise trade volume growth to 0.5 percent, citing the expected delayed impact of US tariffs.

It marked a significant revision down from its previous estimate in August of 1.8 percent growth.

Trump's tariff policies have also put pressure on global trade rules agreed under the World Trade Organization.

In April, a former WTO boss said the future terms of global trade could be decided outside the 30-year-old international watchdog unless it reforms itself fast.