Reuters reported on Thursday that it had followed the Liberia-registered Marshal Z vessel for five weeks with its satellite supported shipping tracking software. The news agency reports that the ship unloaded some 130,000 tonnes of Iranian fuel into tanks near the Chinese city of Zhuoshan in Zhejiang province.
The unloading of the fuel oil took place less than two weeks after a US imposed deadline on export wavers, set for 1 May, expired.
Several countries, including Japan and China, were granted waivers that allowed them to continue trading with Iran after US President Donald Trump had announced that he was unilaterally walking away from the 2015 Iran Nuclear deal, and re-imposed sanctions.
Earlier, China formally complained to the US over the end of the sanction waivers, with Chinese Foreign Ministry Geng Shuang saying Washington’s decision would “contribute to volatility in the Middle East and in the international energy market.”
The State-owned oil giants Sinopec Group and China National Petroleum Corp both spent billions of dollars on Iranian oilfields, including Yadavaran and North Azadegan.
China is the largest importer of Iranian crude oil.
The US and China are currently in a involved in a suffocating trade war, with tit-for-tat tariffs mounting up to hundreds of dollars.
The dispute sharpened this week after Trump stepped up his battle against Huawei, effectively barring the Chinese telecom giant from the US market and adding it to a blacklist restricting US sales to the firm.
Meanwhile, Iranian Foreign Minister Mohammed Javad Zarif has arrived in Beijing.
The Iranian Mehr news agency reported that his visit would focus on the nuclear deal and the US sanctions against Iran.
China is one of the five remaining parties to the Iran nuclear deal, in addition to Britain, France, Germany and Russia.