China has rejected a demand by the United States to cut Iranian oil imports, according to Bloomberg news agency, which cited two officials familiar with the negotiations.
Beijing, however, agreed not to increase purchases of Iran's crude, the officials, who spoke on condition of anonymity told Bloomberg on Friday.
Francis Fannon, US assistant secretary of state for the Bureau of Energy Resources, was recently in China to discuss sanctions, Bloomberg said, citing a US government official.
US President Donald Trump announced in May Washington's withdrawal from a landmark multinational nuclear deal with Iran.
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.
In return, United Nations-approved sanctions were lifted, and Iran was allowed to resume trading oil and gas on the international market.
As an original signatory, the US also pledged to waive secondary sanctions as long as Iran continued to abide by the deal.
But Trump, a longtime critic of the deal who succeeded Barack Obama as president last year, pulled out of the pact despite repeated assurances by UN inspectors that Iran is in compliance with its obligations.
Washington also imposed a series of additional sanctions on Iranian entities and individuals, as well as foreign companies in Iran, squeezing Iran economically. The US also said that it would exert "maximum economic and diplomatic pressure" on other countries to stop buying crude oil from Iran.
In June, the US state department said that countries buying oil from Iran should bring down to zero their Iranian crude imports by the time Washington re-imposes sanctions on November 4.
Iranian President Hassan Rouhani has warned the US against any attempt to stop Tehran's oil trade, threatening to block the strategically important Strait of Hormuz.
"The Americans say they want to reduce Iranian oil exports to zero ... It shows they have not thought about its consequences," Rouhani was quoted as saying by state news agency IRNA while on an official visit to Austria's capital, Vienna, in July.
"Iran will survive this round of US sanctions as it has survived them before," Rouhani said, describing them as a "crime and aggression".
Rouhani says US unaware about consequences of Iran oil ban
Also last month, China, which is Iran's biggest customer, said it did not accept unilateral sanctions against Iran.
"The unilateral sanctions should be abandoned because they are counterproductive," Chinese Foreign Ministry spokesperson Hua Chunying told reporters.
"China and Iran unwaveringly maintain normal trade and economic ties. China will continue to cooperate with Iran adhering to its international obligations," she added.
In July, Beijing lifted monthly oil imports from Iran by 26 percent. This accounted for 35 percent of Iranian exports last month, according to ship-tracking data compiled by Bloomberg.