The United States says it is prepared to impose sanctions on all countries that continue to buy Iran's oil -- including China -- after Washington starts restoring bans on the Islamic Republic’s energy sector.

The announcement was made on Thursday by Brian Hook, the head of US State Department's newly-established Iran Action Group, after he was asked by reporters about the group’s plan for dealing with China, The Wall Street Journal reported.

“The United States certainly hopes for full compliance by all nations in terms of not risking the threat of US secondary sanctions if they continue with those transactions,” he said.

“We are prepared to impose secondary sanctions on other governments that continue this sort of trade with Iran,” Hook noted.

He said the US would issue waivers from sanctions only to countries that had made efforts to reduce their oil purchases from Iran.

Back in May, the US withdrew from a 2015 multilateral nuclear agreement with Iran and said it would re-introduce the sanctions that had been lifted under the accord.

Washington reinstated a series of unilateral sanctions against Iran in early August and would re-impose a second batch in November which would primarily be meant to undermine Tehran’s oil exports.

Beijing, Iran’s top oil customer has thus far been defiant to Washington's call to stop buying Iranian oil, saying commercial cooperation between the two sides did not harm other countries' interests and therefore had to be protected from sanctions.

In a statement earlier this month, China’s Foreign Ministry said Beijing's business ties with Tehran were "reasonable" and did not breach UN resolutions.

It also expressed opposition to Washington’s sanctions against Iran as well as what it described as “long-armed jurisdiction."

In July, the Wall Street Journal cited senior American officials as saying they believed that China was likely to buy even more Iranian crude after the sanctions.