The US has warned that it will impose sanctions on China if Asia’s largest economy continues to import crude oil from Iran.

A US Department of State spokeswoman said yesterday that sanctions would be placed on any country that continues to import Iranian crude in violation of US sanctions.

"We're going to zero, and countries that don't abide by US sanctions will face repercussions for not abiding by US sanctions," said Department of State spokeswoman Morgan Ortagus during a briefing held on Thursday.

"That goes for China or any other country in the world. We expect all countries to abide by US sanctions."

US officials believe the push for maximum pressure on Iran is being weakened by ongoing crude flows between Iran and China.

China is Iran’s largest crude customer, importing an estimated 150,000-200,000 barrels per day (bpd) according to S&P Global Platts data.

Iranian crude and condensate exports, which averaged about 1.7 million bpd in March, fell to about 1 million bpd in April and an estimated 800,000 bpd in May, according to collective data reported by S&P Global Platts.

The majority of May’s sales were to China, Turkey and Syria.

Sanctions waivers given to Iran's largest crude and condensate buyers expired in early May and have not been renewed.

S&P Global Platts Analytics forecasts Iranian exports will average 450,000 bpd in the second half of 2019.

Exactly how the US intends to sanction China without impacting the global economy remains to be determined.

Increased US pressure on Iranian crude exports comes during a tense week that has seen a Ukrainian-owned VLCC seized in Gibraltar over an alleged cargo of Iranian oil to Iran, and claims of the Iranian naval forces harassing a BP suezmax tanker in the Strait of Hormuz.