Only 12 vessels crossed the Strait of Hormuz in the past 24 hours, NBC News reported on Tuesday, citing MarineTraffic data.
Four of the vessels were sailing under the Iranian flag and most of the 12 vessels used the Iranian-approved route off Bandar Abbas, according to the report.
Greek risk management firm MARISKS said unknown actors posing as Iranian authorities had contacted companies whose vessels are stuck west of the strategic waterway, asking for transit fees in Bitcoin or Tether in return for “clearance.”
"These specific messages are a scam," the firm said in an alert, adding the communications did not originate from Iranian authorities.
The warning comes as the United States continues a blockade of Iranian ports, while Iran has imposed restrictions on the Strait of Hormuz, a key chokepoint through which about a fifth of global oil and liquefied natural gas once passed before conflict disrupted flows.
Amid ceasefire talks, Tehran has suggested collecting tolls from vessels seeking safe transit, contributing to uncertainty among shipowners.
Hundreds of vessels and roughly 20,000 seafarers remain stranded in the Persian Gulf due to the disruptions, according to the firm.
On April 18, when Iran briefly allowed limited passage subject to inspections, several ships attempted to transit, but at least two vessels, including a tanker, reported that Iranian boats fired shots, forcing them to turn back.
MARISKS said it believed at least one ship that came under fire while trying to leave the strait on Saturday may have been affected by the fraudulent scheme.
The messages cited by the firm said vessels would need to submit documents for review by Iranian security services, after which a cryptocurrency fee would be set before transit at a pre-arranged time.