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June 1 (Reuters) - Goldman Sachs has raised its copper price forecast on Monday for end of 2026 to $13,735 per metric ton from $12,465, citing a tighter-than-expected global market outside the U.S. due to weaker mine supply growth and stronger U.S. imports.

The bank also increased its average 2027 copper price forecast to $13,800 per ton, up from $12,150. It now expects copper markets outside the U.S. to face supply deficits of approximately 640,000 tons in 2026 and 170,000 tons in 2027, significantly higher than its previous estimates.

The revised outlook is driven primarily by weaker production growth globally, which is expected to curb overall copper availability. At the same time, the United States is projected to increase imports, effectively drawing the metal away from other regions.

Meanwhile, Goldman forecasts U.S. copper inventories to increase by around 900,000 tons this year, compared with an earlier estimate of 550,000 tons, as rising imports absorb available global supplies. The bank's base case assumes no U.S. copper import tariffs in 2026.

Combined output from key mines such as Grasberg in Indonesia and Kamoa-Kakula in the Democratic Republic of Congo is now expected to fall short by about 200,000 tons, than previously forecast. Both mines are not expected to return to full capacity before 2028.

Goldman expects copper prices to remain near current levels of around $13,600 in the coming months but outlined several potential risks.

A prolonged closure of the Strait of Hormuz could weaken prices to around $12,600 by late 2026, while the introduction of U.S. copper tariffs could push prices above $14,000 in the second half of 2026. Conversely, a clear decision against tariffs could see prices ease to approximately $12,800 in 2027 as supply pressures moderate.