The first oil supertanker in almost a month has been spotted moored at Iran’s main crude-export facility in the northern Persian Gulf, highlighting the largely effective nature of an American blockade on Tehran’s shipping.

An image taken by the European Union’s Sentinel 1 satellite shows a vessel with the dimensions of a very large crude carrier, or VLCC, alongside a jetty to the west of Kharg Island on the  morning of June 2. No similarly sized ships had been observed at the island since May 6.

The collapse in loading activity suggests that Tehran might have used up its available tankers amid the U.S. blockade that began in mid-April, or chosen not to fill ships without knowing they would be able to get to global markets. Prior to the cordon, such loadings happened almost every day.

It remains to be seen if the ship will escape from the Persian Gulf. No Iranian crude exports passed through Washington’s blockade in May, United Against Nuclear Iran, a nonprofit, said in a report viewed by Bloomberg News.

The blockade is depriving Tehran of petroleum revenue and the market of millions of barrels of supply. Prior to the U.S. measures, Iran was by far the largest country exporting its crude because the Islamic Republic had prevented other countries’ ships from using the Strait of Hormuz.

Since May 6, the EU’s Sentinel 1 and 2 satellites have taken images of Kharg on 17 out of 26 days. Only one gap in images — between May 21 and May 24 — would have been long enough for a supertanker to have loaded undetected.

Separately, the U.S. Navy “enforced blockade measures against Botswana-flagged M/T Lexie as it transited international waters toward Kharg Island,” firing a missile into its engine room, U.S. Central Command said in a post on X on Tuesday. The vessel is spelled Lexi, flying a false Comoros flag, on some shipping platforms.

The U.S. Navy imposed a blockade of all maritime traffic entering and exiting Iranian ports on April 13 and has since disabled six commercial vessels and redirected 122, CENTCOM said in the same post.