China, India and Japan are planning cuts of at least 10% in Iranian crude oil imports as tightening US sanctions make it difficult for the top Asian buyers to keep doing business with the Opec producer.

The countries together buy about 45% of Iran's crude exports. The reductions are the first significant evidence of how much crude business Iran could lose in Asia this year as Washington tries to tighten a financial noose around Teheran.

The cuts would add to an EU ban on Iranian oil imports, which comes into effect on July 1, to restrict the flow of vital foreign exchange to Teheran, which is under pressure because of its nuclear programme.

Japan is close to an agreement with Washington on the size of cuts needed to win waivers from the US sanctions, two ministers said. The Yomiuri newspaper, citing an unidentified source, said the two sides would settle on an 11% cut.

The Indian government is pushing its refineries to cut imports by at least 10%, two sources said. India has said it will not abide by US unilateral sanctions so its response could indicate the increasing uncertainty about doing business with Iran.

China's Unipec, the trading arm of Sinopec, is likely to cut imports by 10% to 20% under 2012 supply contracts, said a Chinese industry executive with direct knowledge of the deal.

China had already cut back sharply on Iran crude purchases in the first quarter of this year while it haggled over full-year supplies contracts.

Taking those cuts and planned purchases by China's only other major importer, Zhuhai Zhenrong, into account, China's total cuts in purchases of Iranian crude oil this year will amount to about 14%.

In a further blow to Teheran, East Asian purchases of Iranian fuel oil are likely to slump to a six-month low next month, according to comments by Singapore oil traders and an examination of shipping reports.