Report: U.S. Navy Destroyer Turns Back Two Iran-Linked Tankers

The U.S. blockade of Iranian shipping is unfolding successfully so far, according to U.S. Central Command, including enforcement along the Gulf of Oman coastline. Two tankers that attempted to leave Chabahar were interdicted by a U.S. Navy destroyer and instructed to turn around, officials told Reuters late Tuesday. Separately, officials told the New York Times that six Iran-linked vessels had turned around after U.S. forces contacted them by radio and directed them to return to an Iranian port.

Inbound traffic may be harder to police, as tankers transiting the strait on a westbound voyage could in theory call in any Gulf country. In practice, most of Iran's exports are served by a separate fleet of "shadow" tankers, many of them sanctioned by the U.S. government; Iranian barrels are the only cargo available in the Gulf for these blacklisted ships.

One of these sanctioned vessels has slipped through the U.S. Navy blockade, transited the Strait of Hormuz and arrived in Iran, TankerTrackers.com reported late Tuesday - with AIS turned on throughout the voyage. (The consultancy did not name the tanker involved.) Shortly after, U.S. Central Command claimed in a statement that "U.S. forces have completely halted economic trade going into and out of Iran by sea."

The blockade explicitly exempts traffic to and from all other Gulf ports, and the more risk-tolerant shipping interests appear to accept the new arrangement. Over 20 neutral vessels have transited the Strait of Hormuz since Monday, two U.S. officials confirmed to the Wall Street Journal. AIS data shows little movement, and the officials confirmed that some of the ships were making the crossing without broadcasting their positions.

Effects on Iranian oil

The blockade's objective is to clamp down on seaborne exports of Iran's oil - a reversal of last month's policy. In March, the administration issued a blanket waiver that temporarily lifted sanctions on Iran's seaborne oil in order to speed its delivery to market, intending to stave off rising global oil prices. Now, the U.S. Treasury is reverting to "maximum pressure" on Iran's oil exports and the entities that enable them. In a statement, Treasury said that it is "moving aggressively with Economic Fury" and stands ready to impose secondary sanctions on foreign banks that enable Iran's energy industry.

"The short-term authorization permitting the sale of Iranian oil already stranded at sea is set to expire in a few days and will not be renewed," the Treasury said in a statement.

The secondary effects of the blockade and sanctions enforcement could include shut-ins in Iran, the first since the conflict began six weeks ago. Other Gulf nations have been forced to cut production because of a lack of onshore tank storage and a lack of tankers to load; now Iran is also cut off from a supply of empty tankers. If the U.S. blockade continues, the National Iranian Oil Company will eventually have to begin shutting in wells as onshore storage begins to run out. Like Kuwait, the UAE, Saudi Arabia and Iraq - already affected by Iran's earlier blockade - Iran would then face the protracted and challenging process of restarting wells, adding weeks or months before full normalization of production.