Iran’s main oil-loading terminals have remained empty for weeks, adding to signs that a US naval blockade of the country is throttling Tehran’s exports.

No tankers have docked at Kharg Island’s crude-export terminals since late August, an analysis of ship-tracking data and European Union satellite images shows. That’s the longest stretch of inactivity at the island since the start of the US-Iran war in February.

The lack of tankers at Kharg, deep inside the Persian Gulf, points to the increasing pressure on Iran since the US renewed its military blockade of the country’s shipping three months ago. Crude exports have plunged from almost 1 million barrels a day in July to nothing since late August, according to vessel-tracking data compiled by Bloomberg and figures from Kpler and Vortexa.

July’s loadings were concentrated in the first half of the month, after a ceasefire deal between Washington and Tehran temporarily lifted the US blockade. No tankers laden with Iranian crude have managed to leave the country or nearby waters since the middle of that month, when the shipping ban was reimposed, nonprofit group United Against Nuclear Iran said.

Iran exported nearly 650 million barrels of crude in the year through April, with most ending up in China, tanker-tracking data show. Now, as Tehran’s oil disappears from global markets, Chinese refiners are turning to other sources of crude and competing with other buyers for barrels and ships. That’s pushed oil prices higher and fueled a historic rally in freight.

As Iran has been thwarted in its attempts to export its production, Tehran has stepped up attacks on vessels transiting the Strait of Hormuz, which connects the Persian Gulf to the open seas. In the first two weeks of October, 25 ships were targeted in and around the chokepoint, compared with 18 incidents reported for the whole of September and 15 in August, according to alerts sent out by UK Maritime Trade Operations, a unit of the country’s navy.

Kharg Island handles almost all of Iran’s crude exports, with Jask — a port at the eastern end of Hormuz — accounting for just a small percentage of the trade. While Kharg has been idle, no tankers have been seen berthed at Jask either, the satellite images show.

The images reviewed by Bloomberg News were taken from the EU’s Sentinel 1 and 2 orbiters. They pass separately over the island every few days, and the longest gap between any of their images was three days. It typically takes about 24 to 48 hours to fully load a very large crude carrier at Kharg Island.

A small ship appeared berthed on Oct. 10, seemingly breaking the 40-day period of dormancy. But its automated position signals identified it as the chemicals/products tanker Clavel, which has been shuttling between Iranian ports.

Separately, at least two tankers were seen docked at jetties off Kharg Island’s southeast tip between Sept. 12 and Sept. 15, but those are only used to handle shipments of liquefied petroleum gas and sulfur.