HANOI, March 26 (Reuters) - Vietnam's largest refinery Nghi Son said on Tuesday it will boost its operating capacity by 15% to 20% in order to ensure stable supplies.

The 200,000-barrel-per-day Nghi Son Refinery and Petrochemical is currently operating at 100% of its designed capacity, it said.

The "planned increase of 15 to 20% in the refinery's capacity will further ensure a stable supply of petroleum products," it said in a statement.

Nghi Son is one of two oil refineries in Vietnam, which meet around 70% of the country's needs for refined petroleum products

Nghi Son is 35.1% owned by Japan's Idemitsu Kosan Co , 35.1% by Kuwait Petroleum, 25.1% by Vietnam's state oil firm PetroVietnam and 4.7% by Mitsui Chemicals Inc.

The company has delivered its first batch of 10ppm sulphur diesel oil cargo to the domestic market, it said, without elaborating. (Reporting by Khanh Vu; Editing by Martin Petty)