Washington DC — The US State Department is "doing everything we can to deter and discover" evasion of sanctions on Iran's oil buyers, a top official said Thursday, adding that Tehran's crude exports will fall further "very soon."

Brian Hook, State Department special representative for Iran, said US sanctions on Iran's oil buyers have cut the country's exports by more than 1 million b/d.

"Many more barrels will be coming off very soon," Hook said at a briefing at Joint Base Anacostia-Bolling in Washington, DC.

"All of our diplomatic posts in the region, especially in the Middle East and in Europe, are putting in place strategies to detect and to prevent sanctions evasion," he added.

Iranian crude export loadings are below 800,000 b/d so far for November, compared with a six-month average of 2.4 million b/d earlier this year, according to S&P Global Platts Analytics and data from Platts trade flow software cFlow.

But Platts Analytics expects the actual November average to be higher than 800,000 b/d due to ships increasingly turning off transponders. Average loadings could be closer to 1.1 million b/d this month, given contractual lags in Japan and South Korea.

Platts Analytics expects Iran's exports to stay around 1 million b/d by the next US sanctions deadline in May.

Eight countries received waivers to continue importing Iranian crude through May 4: China, India, Japan, South Korea, Turkey, Taiwan, Greece and Italy. Many of the countries are expected to seek fresh waivers for the six months starting May 5, in exchange for cutting their Iranian imports further.

Hook said the US government is concerned Iran could block two key chokepoints for oil shipments if its influence in the Yemen conflict grows.

About 18.5 million b/d of oil flowed through the Strait of Hormuz and 4.8 million b/d through Bab el-Mandab in 2016, according to the Energy Information Administration.

--Meghan Gordon, meghan.gordon@spglobal.com

--Edited by Jonathan Fox, newsdesk@spglobal.com