* New premiums up 79-81% from Q1

* Marks highest since Q2 2015

* Middle East supply tightening boosts premiums

(Adds details and comments in paragraph 3-12)

By Yuka Obayashi

TOKYO, March 26 (Reuters) - Japanese aluminium buyers

agreed to pay premiums of $350 to $353 per metric ton for

shipments between April and June, the highest in 11 years, as

the Middle East war tightened supply, four sources involved in

the pricing talks said.

Japan is a major Asian 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

serve as the regional benchmark.

The new level is up 79% to 81% from the $195 paid in the

January-March quarter, marking a second straight quarterly

increase and the highest since April-June 2015, when premiums

touched $380.

In late February, global producers offered Japanese buyers

premiums of $220-$250 per ton for the April-June period, up

13%-28% from the current quarter, but later withdrew or let the

offer expire while assessing risks to cargoes transiting the

Strait of Hormuz after the U.S. and Israel attacked Iran on

February 28.

One producer raised its offer to $350 per ton in mid-March

and buyers accepted. Another sought higher levels, but both

sides eventually settled at $353, the sources said.

"Amid concerns the conflict could drag on, we had little

choice but to accept these high prices given the risk of supply

disruptions from the region," a source at a Japanese rolling

mill said.

"If the strait closure continued, Middle Eastern smelters

could struggle to secure raw materials and production may be

affected. We compromised quickly because prices could rise

further the longer we waited," he said.

The sources declined to be identified due to the sensitivity

of the matter.

The Middle East accounts for around 9% of global aluminium

supply, and the war has rattled the market by effectively

freezing shipments through the strait.

Earlier this month, Aluminium Bahrain, which runs

one of the world's biggest smelters, declared force majeure on

shipments, while Qatari smelter Qatalum began shutting down

production.

Japan imported nearly 30% of aluminium ingots, including

primary and alloy, from the Middle East in 2025.

The quarterly negotiations between Japanese buyers and

global miners including Rio Tinto Ltd ( RTNTF ) and

South32 ( SHTLF ) began last month.