TOKYO, July 16 (Reuters) - Some Japanese aluminium buyers have agreed to pay two global producers a premium of $172 per metric ton over the benchmark price for shipments in July to September, up 16%-19% from the previous quarter, four sources involved in the pricing talks said.

The figure is higher than the $145-$148 per ton paid in the April-June quarter but lower than the initial offers of $175-$190 per ton made by producers.

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

The increase from the previous quarter reflected tighter supplies in the region as some metals were diverted to Europe where premiums were higher and demand was stronger, a source at a Japanese trading house told Reuters.

The negotiations are continuing, another source at a producer said.

The sources declined to be identified because of the sensitivity of the discussions.

The quarterly pricing talks began in late May between Japanese buyers and global suppliers including Rio Tinto , and South32.

One producer lowered its offer to $172 per ton late last week after raising it once to $185 from the initial proposal of $175, as the talks were dragging longer than usual, a third source at a Japanese end-user said. The negotiations usually end before the new quarter begins.

Another supplier also brought down its offer this week to $172 per ton from its initial level of $190, the third source said. (Reporting by Yuka Obayashi; Editing by Tom Hogue and Mark Potter)