China, India, Japan and South Korea last month imported about 762,000 barrels per day from Iran, down 56.4% from a year earlier, Reuters reported.
This marks the lowest volume of shipments since October 2013, when an earlier round of tough US and EU sanctions had slashed exports from the OPEC member starting from early 2012.
In reimposing sanctions on Nov. 5 on Iran's energy and shipping industries, however, Washington also granted exemptions to China, Japan, South Korea and five other countries, allowing them to continue buying some Iranian oil for at least another 180 days.
India's imports of Iranian oil dropped the least, falling just 0.2% from the same month last year to 466,400 bpd.
Most India refiners boosted purchases from Iran ahead of the US sanctions as Iran was offering almost free shipping and extended credit periods.
South Korean oil imports from Iran, though, fell to zero for a second straight month in October. Japan's oil imports from Iran plunged by 71% to a six-month low of 48,033 bpd last month.
China's imports of Iranian crude tumbled 64% in October to 247,200 bpd.