By Yuka Obayashi

TOKYO, March 3 (Reuters) - Global aluminium producers have pulled initial premium offers to Japanese buyers, or let them expire, as they gauge a threat from escalating Middle East conflict to cargoes through the Strait of Hormuz, four sources involved in quarterly pricing talks said.

Japan is a major Asia-based importer of the metal and the premiums for primary metal shipments it agrees to pay each quarter over the London Metal Exchange (LME) cash price CMAL0 set the benchmark for the region.

Last week, South32 S32.AX and Rio Tinto RIO.AX, RIO.L offered Japanese buyers premiums of $220 and $250 per metric ton respectively for April–June shipments, up 13% to 28% from the current quarter, mirroring higher overseas premiums.

South32's offer expired on Friday, before the conflict intensified, while Rio withdrew its offer on Monday, saying it needed to evaluate potential disruptions, the sources said.

All four sources spoke on condition of anonymity as the matter is a sensitive one.

Rio Tinto declined to comment.

Even a short-term shortage of supply could drive up regional aluminium premiums for months if it means the benchmark for the quarter is set at higher levels.

"Production of aluminium in the Middle East, including the United Arab Emirates and Bahrain, appears unaffected," a source at a producer said.

"But, should the closure of the Strait of Hormuz persist, shipments could be delayed, potentially tightening global supply, including in Asia," the source added.

"We are monitoring the situation now, but plans to set the April-June quarter premium by the end of March remain unchanged," the source said, adding that the producer plans to issue a new offer as soon as possible.

Even if the Strait remains closed, alternative shipping routes appear to be available for the UAE's supply, and alternative sourcing from other suppliers in Asia is also possible, a second source at a trading house said.

"Should hostilities persist, it will become necessary to consider alternative measures," he added. "While procuring primary metals may be manageable, securing substitutes for value-added products is likely to prove difficult."

Japan imported about 20% of primary aluminium ingots from the Middle East in 2025.

For the quarter from January to March, Japanese buyers agreed to pay a premium of $195 per ton PREM-ALUM-JP, up 127% from the prior quarter, reflecting fears over tightening supply.

Quarterly pricing talks between Japanese buyers and producers began last week and are expected to continue later this month.

(Reporting by Yuka Obayashi in Tokyo; Additional reporting by Melanie Burton in Melbourne; Editing by Clarence Fernandez)

((Yuka.Obayashi@thomsonreuters.com; +813-4563-2761;))