The country began tapping its stockpiles, the world's largest, in March as the government looked to temper a spike in prices caused by the hit to supply from the Middle East war.

"To ensure the stable supply of crude oil, we will release starting in early May the equivalent of roughly 20 days' worth (of oil) from the national reserves," she said at a meeting held in response to the conflict in the Middle East.

It will be the second release from the state oil reserves, while it has also tapped 15 days worth of private-sector petroleum stockpiles.

Japan depends on the Middle East for around 95 percent of its oil imports.

A joint reserve is held in the country by Saudi Arabia, the United Arab Emirates and Kuwait, according to the Petroleum Association of Japan.

Under normal circumstances, the jointly stored crude is commercially used, but in the event of an emergency, Japanese oil companies have preferential purchasing rights.

Members of the International Energy Agency agreed on March 11 to tap oil stockpiles to cushion the surge in prices -- by far the largest-ever response of its kind.