Japan, historically one of Iran's largest trading partners, has cut its oil imports from the Islamic Republic by 40% in five years, a Japanese official said Thursday, underscoring the impact of international sanctions against Tehran.

Asked about
Japan 's Iranian oil imports, Yutaka Yokoi, a Japanese foreign ministry official, said they are getting "smaller...We have reduced imports over five years by 40% from Iran because of U.S. sanctions."

Last year,
Washington banned oil transactions with Iran 's Central Bank as part of a broad range of existing sanctions to pressure Iran over its nuclear program. The move forced Iran 's Asian oil buyers to cut their purchases in exchange for an exemption permitting dealings with the Bank.

Tehran 's sales to Asia --its last major market following the U.S. and European Union embargoes--have also been hit by an EU insurance ban on Iranian oil shipping and international sanctions on Iran 's commercial banking sector.

Independent experts and Iranian lawmakers say oil exports have been more than halved to about 1 million barrels a day at present from at least 2.2 million barrels a day early 2012.

Mr. Yokoi, who was speaking during a briefing on the Japanese Prime Minister Shinzo Abe's visit to the
United Arab Emirates and Saudi Arabia , said more than 80% of Japan 's oil imports are from the Middle East , but that it had switched some of its supply from Iran to Saudi Arabia and the U.A.E.