TOKYO (Reuters) - Japanese trading house Mitsubishi Corp has renewed its annual oil purchase deal with Iran but cut the loading volume to comply with U.S. sanctions against the Islamic Republic, trade sources said on Friday.

Mitsubishi's new contractual volume from April onwards remained unclear. The company had bought 15,000 barrels of crude per day (bpd), or more, last year.

As Western nations tighten curbs in their bid to curtail Tehran's nuclear program, Iran's crude exports in April and May have fallen by 1 million bpd since the end of 2011 to 1.5 million bpd, the International Energy Agency said last week.

Mitsubishi Corp did not confirm the renewal, with a company spokesman declining to give any details.

Mitsubishi loaded some barrels of Iran oil in the period from April to June, the sources said. Japan's top two buyers of Iranian oil, Showa Shell Sekiyu or/and JX Nippon Oil & Energy should have bought the barrels, they added.

Besides Mitsubishi, another trading house, Toyota Tsusho has been also lifting Iranian crude since April for the top two buyers, the sources added.

Japan nominated loadings of 120,000 bpd for both June and July, sources said, unchanged from May but down significantly from a year earlier, to comply with global sanctions against the Islamic Republic.

Iranian oil accounted for nearly 9 percent of Japan's crude imports last year. Japan has reduced the flow already to comply with U.S. sanctions requiring buyers to make sizeable cuts, but wants to avoid more drastic reductions that could drive up energy import costs and hurt the world's third-largest economy.