The global economy is set to slow sharply in 2026 after the war with Iran disrupted energy supply chains and triggered a fresh bout of inflation, the International Monetary Fund warned on Wednesday.

The forecasts reflect the damaging toll from the decision by the United States and Israel to attack Iran this year. Those attacks spurred Iranian retaliation on energy infrastructure in the region, destabilizing a world economy that had already been rocked by the Covid-19 pandemic and Russia’s war in Ukraine.

Global output is poised to fall to 3 percent in 2026 from 3.5 percent last year, according to an update for the I.M.F.’s World Economic Outlook. That is slightly slower than the fund’s April projection of 3.1 percent growth, underscoring the protracted nature of the conflict.

The forecasts remain subject to considerable uncertainty. Attacks on tankers trying to transit the Strait of Hormuz this week have raised doubts about the durability of the recent cease-fire between the United States and Iran, and on Tuesday the United States rescinded a waiver on sanctions that would have allowed more Iranian oil to be sold on global markets.

President Trump cast doubt on the truce at a NATO meeting in Turkey on Wednesday when he said, “I think it’s over.”

Shipping traffic through the strait was obstructed for months, sending energy prices higher and pushing up consumer prices around the world. The I.M.F. expects global inflation will rise to 4.7 percent in 2026 from 4.1 percent in 2025 because of elevated commodity prices.

Although the 2026 outlook is slightly darker, the I.M.F. said the global economy was proving to be relatively resilient. Global growth in the first quarter of the year was stronger than projected, as renewable energy helped blunt the effect of higher oil prices and investments in artificial intelligence powered output.

“The global economy as a whole has, so far, weathered the shock from the war better than feared,” the I.M.F. economists wrote in the report.

Oil-producing countries in the Middle East have been hit hardest by the war and are expected to face sharp contractions this year.

The outlook for Iran, however, was modestly upgraded since April as U.S. sanctions on its oil exports were temporarily relaxed. This week, the Trump administration revoked a 60-day license allowing the sale of Iranian energy products after tankers were attacked trying to pass through the Strait of Hormuz.

Nations that consume the most energy are also facing an output crunch from higher oil prices. Growth in India is expected to decline to 6.4 percent this year from 7.7 percent in 2025. Output in China is projected to decline to 4.6 percent in 2026 from 5 percent last year.

Output projections in the United States held steady from April at 2.3 percent, as oil exports and technology investments buttressed growth.

High gas prices have been a political concern in the United States, but Kevin M. Warsh, the new chairman of the Federal Reserve, said last week that inflation risks had eased in the weeks since he took over. Speaking at a gathering in Europe last week, he reiterated his pledge to deliver price stability after an extended period in which the central bank had missed its 2 percent target.

The I.M.F. urged policymakers to remain focused on price stability as they assess the effect of volatile commodity prices and growing demand for new A.I. technology.