US MARAD said that since early May there had been an increased possibility of Iran or its regional proxies taking action against US and partner interests.

These included oil production infrastructure, after Tehran threatened to close the vital Strait of Hormuz chokepoint through which about one third of the world’s seaborne crude exports flow, according to MARAD.

Iran or its proxies could respond by targeting commercial vessels, including oil tankers, or US military vessels in the Red Sea, Bab-el-Mandeb Strait, or the Persian Gulf.  Reporting indicates heightened Iranian readiness to conduct offensive operations against US forces and interests,

...MARAD said.

Millions of barrels of oil pass daily through the various bottlenecks from Middle East oil producers to markets across the globe, Reuters reports.

Tensions have risen between US and Iran, since the Trump administration withdrew a year ago from the 2015 JCPOA (Joint Comprehensive Plan of Action), the international nuclear deal with Iran, and began ratcheting up sanctions to throttle Tehran’s economy.

MARAD added that US-flagged ships were encouraged to contact the Fifth Fleet - which is tasked with protecting commercial shipping in the area - at least two days before sailing through the Strait of Hormuz.

Washington further tightened sanctions on Iran this month - eliminating waivers that had allowed some countries to buy its oil - with a goal of reducing Tehran’s crude exports to zero.

Iran has responded by scaling back some curbs on its nuclear program concerning material stockpiles though it remains compliant with commitments to restrict its uranium enrichment activity.

Last week, US President Donald Trump provided an executive order banning the purchase of Iranian iron, steel, aluminum and copper, worsening the tensions with the Islamic Republic a day after he declared he may begin enriching uranium again in two months.