Francis Fannon, U.S. assistant secretary of state for the Bureau of Energy Resources, was recently in China to discuss sanctions, Bloomberg said, citing a U.S. government official.
The U.S. has told all countries, including India to stop their oil imports from Iran by November 4 or face sanctions for carrying out any transaction with Tehran as there would be "zero" waivers to any country.
Under the 2015 pact, signed by the US, UK, Britain, China, Russia and the European Union, Tehran agreed to scale back its uranium enrichment programme.
Monday's rise in oil costs continues a bounce from last week's low of 66.90, and United States crude prices are making a run for the last swing high of 69.33, though the recent peak of 70.40 remains just out of reach, with support from Friday's bottom of 67.85.
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.
Washington has also threatened to punish companies that do not stop importing Iranian oil by November 4, when sanctions on the country's oil, gas and shipping industries are set to be imposed.
The biggest member of the Organization of Petroleum Exporting Countries pumped 10.3 million barrels a day in July, according to the delegates, who asked not to be identified because the data is private.
Iranian President Hassan Rouhani has warned the USA against any attempt to stop Tehran's oil trade, threatening to block the strategically important Strait of Hormuz.
Trump unilaterally withdrew the USA from the multilateral deal with Iran in May and announced plans to reimpose sanctions on the Islamic Republic, that would eliminate Tehran's oil revenues.
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.
"China and Iran unwaveringly maintain normal trade and economic ties".
Between April and July India's oil imports from Iran has risen by an annual 40% to about 677 500 bpd, the data showed.
India's July purchases of Iran's oil were about 85 percent higher in comparison to the shipments of about 415,000 bpd a year earlier, the news agency said.
What's next for Iran oil?