Imports of crude oil by Iran's four major buyers in Asia more than doubled in December compared with the same month a year earlier, for the third straight month, with purchases by South Korea up seven-fold and India's more than three times higher.
Iran's top four Asian buyers - China, India, South Korea and Japan - imported 1.89 million barrels per day (bpd) last month, data from governments and ship-tracking services showed.
In absolute terms, imports slipped for a second consecutive month, from a peak of just under 2 million bpd in October, which was the highest since at least 2010, according to data by International Energy Agency.
Iran was exempted from an OPEC deal in January to reduce output by 1.2 million bpd, a boon for Tehran which had argued it needs to regain the market share it lost under Western sanctions over its nuclear program.
Across the first full year since the sanctions were lifted, Iran has boosted exports to its biggest Asian customers by nearly 60 percent to 1.63 million bpd.
Iran's crude oil imports cost Japan an average $43.87 a barrel for December, the third cheapest after Ecuador and Columbia, trade data from Japan's Ministry of Finance showed.
Japan's trade ministry on Tuesday released official data showing its imports jumped more than 40 percent from a year earlier to 246,243 bpd last month.
China's imports rose 30 percent to 689,530 bpd, meaning the country regained top spot among consumers after buying less than India for three consecutive months.
India's imports grew to 546,600 bpd, while South Korea's purchases rocketed to 410,387 bpd.
Iran's total monthly oil exports are set to climb slightly in February from January, as Indonesia takes its first shipment since sanctions were lifted, a person with knowledge of Iran's tanker loading schedule told Reuters last week.
January exports were set to fall to the lowest since July at about 2.16 million bpd, with February loadings likely to be just over 2.2 million bpd, according to the person, who spoke on condition of anonymity.