TOKYO (Kyodo) -- Japan on Thursday began a review of its rice policy after soaring grain prices hit consumers, aiming to boost production and prevent supply shortages.

Prime Minister Shigeru Ishiba pledged to ensure stable rice supplies, as prices have doubled over the past year, prompting the release of massive stockpiles to curb the surge.

The government held its first meeting of relevant ministers to examine why the price uptrend, initially triggered by a poor harvest, has persisted and to explore possible responses.

While Japan no longer directly controls rice output through its long-running acreage reduction policy, it still sets target production levels based on expected demand and offers subsidies to encourage farmers to grow other crops.

In that environment, small fluctuations in rice harvests can lead to big swings in prices, experts say.

The number of "rice farmers is expected to decline sharply going forward, and Japanese people are increasingly worried about the supply of the staple food, as rice prices surged due to last summer's shortage," Ishiba said at the meeting.

"It's important for us to ensure stable rice supplies," he added.

The meeting came as rice released from government reserves began hitting store shelves at roughly half the recent average price of around 4,300 yen ($30) per 5 kilograms in May.

The government has moved to sell it directly to retailers rather than through auctions, which were blamed for keeping retail prices high. In total, 610,000 tons will be released, about two-thirds of the government's stockpiled rice.

As public frustration has grown over soaring rice prices, Ishiba has argued that production should be increased to help ease consumer concerns as part of his push to reform the agriculture sector.

Farm minister Shinjiro Koizumi, who has vowed to deliver cheaper reserve rice to consumers more broadly, said the government should also discuss creating a "safety net" and extending support for farmers vulnerable to price swings.

Koizumi told reporters that the government should take a fresh look at its export policy and support mechanism.