A State Department official confirmed Francis Fannon, assistant secretary of state at the US Bureau of Energy Resources, was recently in China to discuss Iranian sanctions.
However purchases from Iran could slow from now on; last month, state-run Hindustan Petroleum Corp Ltd (HPCL) was forced to cancel an Iranian oil shipment as insurers were not willing to provide cover for its two refineries for processing Iranian oil, sources with knowledge of the matter said.
In May, Trump controversially pulled America out of the nuclear deal Obama agreed with Iran in 2015.
Global benchmark Brent crude fell on Thursday as concerns about mounting supply returned after a brief rally on comments that Saudi Arabia's exports would fall in August.
But Trump, a long-time critic of the deal who succeeded Barack Obama as president past year, pulled out of the pact despite repeated assurances by United Nations inspectors that Iran is in compliance with its obligations.
The US is due to impose a series of new sanctions on Iran in the next few months.
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Recall that President Hassan Rouhani of Iran had earlier warned the U.S. against any attempt to stop Tehran's oil trade.
USA officials have softened their stance after initially saying they would press allies in Europe, Asia and the Middle East to adhere to the sanctions and reduce their imports to zero.
Oil traders had anticipated that sanctions would take Iranian barrels off the market, said Rob Haworth, who helps oversee $151 billion at US Bank Wealth Management in Seattle.
Also last month, China, which is Iran's biggest customer, said it did not accept unilateral sanctions against Iran.
Chinese Foreign Ministry spokeswoman Hua Chunying said: "China and Iran unwaveringly maintain normal trade and economic ties".
China imports more Iranian oil than any other country. This is causing investors to continue to trim net length, take profits as well as de-risk that position with the sense that oil's upside is limited unless there is material reduction in Iranian barrels.