US officials, speaking to Reuters on condition of anonymity, said the drills appeared created to send a message to Washington, which is intensifying its economic and diplomatic pressure on Tehran but so far stopping short of using the USA military to more aggressively counter Iran and its proxies.
While South Korea has halted imports from Iran and reports in India indicate it may also bow to the United States campaign, Washington's entreaties to Beijing have proved fruitless, two unnamed officials told Bloomberg.
Iran has been furious over U.S. President Donald Trump's decision to pull out of an global agreement on Iran's nuclear program and re-impose sanctions on Tehran.
State refiners accounted for about four-fifth of Iranian oil imports in July with Indian Oil Corp along with its unit Chennai Petroleum Corp getting about 300,000 bpd oil from Tehran, the preliminary data showed.
Preliminary tanker arrival data cited by Reuters on Thursday showed that the Asian country increased purchases of Iranian crude by about 30 percent to a record 768,000 barrels per day (bpd) as state refiners' intake surged ahead of USA sanctions in November.
The Iranian rial has dropped to a record low amid growing concerns about renewed USA sanctions, which kick in on Monday.
Trump made that much known in a Twitter post days ago during a joint White House news conference with Italian Prime Minister Giuseppe Conte.
To keep its shipment flowing Iran has offered insurance for oil cargo and ships to supply oil to India, its top oil client after China.
The spokesperson then pointed to the worldwide anger at the U.S. and Washington's policies towards its age-old allies, saying, "There is indication even in the Persian Gulf littoral states that there are concerns about Trump's policies, because they have the feeling that Trump is only seeking to empty their pockets".
Following Trump's decision to quit the historic Iran nuclear pact on May 8, the United States vowed to reimpose sanctions lifted under the accord against Iran and inflict punishments like secondary sanctions on nations that have business links with Iran.
Tehran has said if it can not sell its oil, other regional countries would not be able to do so neither, triggering speculation that Tehran may block the Strait of Hormuz, through which many worldwide oil cargoes pass.
Sanctions will also be reapplied to USA imports of Iranian carpets and foodstuffs and on certain related financial transactions.
Chinese Foreign Ministry spokeswoman Hua Chunying said: "China and Iran unwaveringly maintain normal trade and economic ties".
The official confirmed that during July delegations would be dispatched to Beijing and Delhi to press home the case, having already visited the capitals of other major Iranian oil importers. "China will continue to cooperate with Iran adhering to its worldwide obligations", she added.