Iran has boosted the income it gets from crude oil sales in non-US dollar currencies to more than 70 percent, an oil official said.

A switch in payment by Nippon Oil and other Japanese refiners to yen has helped the Islamic Republic towards its goal of maximising oil revenue in currencies other than the dollar while the greenback stays weak.

Mohammad Ali Khatibi, deputy director of international affairs at the state oil company, told the oil ministry's official website Shana that some Japanese refiners have asked for more time to honour Tehran's request.

"Currently, over 70 percent of Iran's crude exports are based on euro and yen instead of dollar," said Khatibi.

For nearly two years, the world's fourth-biggest oil exporter has been reducing its exposure to the dollar, saying the weak US currency is eroding its purchasing power.

In July, the National Iranian Oil Company (NIOC) made an official request to customers in Japan, which imports more than 300,000 barrels per day (bpd) of Iranian crude, to pay in yen.

"Nippon Oil is not the only Japanese refinery which has replaced dollar with yen, but also there are some other refineries that have started this replacement," Khatibi said.

"Others called for one or two months to do that."     Before Japan made the switch, just short of 70 percent of Iran's oil income was in non-US dollar currencies. Iran's total crude oil exports are around 2.3 million bpd. - Reuters