TOKYO, March 20 (Reuters) – Japanese aluminium buyers have agreed to pay producers a premium of $129 per tonne for metal to be shipped during the April to June quarter, reflecting surging U.S. spot premiums, five sources directly involved in the quarterly pricing talks said. The deals represent a 25 percent increase from the $103 per tonne premium in the previous quarter. The premium is the highest in three years and marks the second consecutive quarterly rise. Japan is Asia’s biggest importer of aluminium 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.