TOKYO, May 29 (Reuters) - A global aluminium producer has offered Japanese buyers a premium of $175 per metric ton for July-September primary metal shipments, up 18% to 21% from the current quarter, three sources directly involved in quarterly pricing talks said on Wednesday.

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

For the April-June quarter, Japanese buyers agreed to pay a premium of $145-$148 per ton , up 61% to 64% from the prior quarter. (Reporting by Yuka Obayashi in Tokyo, Additional reporting by Julian Luk in London; Editing by Christian Schmollinger)