The Strait of Hormuz is one of the world’s most strategically vital maritime routes, with about 20% of the world’s seaborne ​crude oil ​and liquefied ⁠natural gas flows passing through it.

Tehran has proposed fees or tolls on vessels passing through the Strait, as part of proposals to end the war with Israel and the US.

The advisory, from Treasury’s Office of Foreign Assets Control, said the US is aware of Iranian threats to shipping and demands for payments to receive safe passage through the Strait.

The warning came as Iran sent its latest proposal for negotiations with the US to Pakistani mediators, a move that could improve prospects for breaking an impasse in efforts to end the Iran war.

OFAC said demands may include several payment options, including fiat currency, digital assets, offsets, informal swaps, or other in-kind payments, such as nominally charitable donations made to the Iranian Red Crescent Society, Bonyad Mostazafan, or Iranian embassy accounts.

“OFAC is issuing this alert to warn US and non-US persons about the sanctions risks of making these payments to, or soliciting guarantees from, the Iranian regime for safe passage,” it said. “These risks exist regardless of payment method.”