SINGAPORE, May 21 (Reuters) - Singapore onshore light and middle distillate stocks jumped on sluggish demand, with gasoline and naphtha inventories surging to a three-month high for the week ending May 20, data from International Enterprise (IE) showed in Thursday.

LIGHTS STOCKS SURGE TO 3-MONTH PEAK

Singapore onshore gasoline and naphtha stocks rose to 9.92 million barrels, their highest in 3 months, on weak spot regional demand.

- Indonesia, Asia's top gasoline importer, has been maximising its term volumes and slashing spot imports. The country needs to buy about 5.5 million barrels of gasoline in June, but its term barrels are able to meet 90 percent of that demand.

- But an open East-West arbitrage window could see gasoline inventories falling in the weeks ahead.

* DIESEL, JET STOCKS AT 7-WEEK HIGH

- Onshore distillates stocks in the city-state climbed 446,000 barrels to 11.69 million barrels even as refinery maintenance was at its peak.

- This reflected weak market demand, with Indonesia restricting diesel imports to paltry levels of 2.4 million barrels for June, down from last year's monthly average of 5.0-6.0 million barrels.

- But supplies have been rising, partly due to China. China's diesel exports hit a new monthly record in April at 510,000 tonnes, customs data showed.

* LOWER ARB CUTS FUEL OIL STOCKS TO MONTH-LOW

- Singapore onshore fuel oil inventories fell 466,000 barrels to their lowest in four weeks at 20.24 million barrels, due to declining Western arbitrage flows.

- Western cargoes landing in Asia in May are expected to fall 18-20 percent from last month as European refiners slash capacity on poor margins.

- Tight capacity in the U.S. Gulf Coast is also absorbing some European barrels bound for this region.

- June and July arbitrage supplies are likely to remain tight, below monthly average volumes of around 3.0 million tonnes.