The plot has thickened around the disappearance of the oil tanker MT Riah, towed to Iranian shores last week, with Panama saying it is revoking the ship’s registration over violation of international rules.

Panama's Maritime Authority on Saturday announced that it initiated the process of withdrawing its flag from the Emirati-based tanker Riah, which vanished south of Iran’s Larak Island.

In a statement cited by Reuters, the authority said that its own investigation into the tanker’s disappearance had found that it “deliberately violated international regulations” by failing to report an unusual situation, presumably its seizure by the Iranian Navy. The authority also condemned the use of Panama-registered vessels for “illicit activities” without ascribing any such specific activity to the Riah.

The tanker went missing from radar screens shortly before midnight last Saturday, when its tracking signal abruptly blinked out. On Tuesday, the Iranian news agency ISNA reported, citing the Iranian Ministry of Foreign Affairs, that the Iranian forces came to a foreign tanker’s rescue after it sent a distress signal. While the name of the tanker was not revealed at the time, the vessel was presumed to be the Riah.

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However, two days later, Iran’s Islamic Revolutionary Guard Corps released footage showing the seizure of the ship with ‘Riah’ and “PANAMA” written on its hull, while accusing the vessel of smuggling fuel.

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Semi-official news agency Fars reported at the time that the Iranian Navy had towed the tanker to the shore upon receiving a distress signal and discovered a haul of petroleum products, allegedly smuggled from Iran, after boarding the ship.

Despite airing the footage, Tehran has never acknowledged that the seized vessel was the Emirati-based Riah.

Other murky circumstances in the story have still not been clarified. While it has been widely reported that the Riah made frequent trips between different emirates of the UAE, that country has distanced itself from the ship.

"The tanker in question is neither UAE owned nor operated,” a UAE official told Emirates News Agency earlier this week.

There is also uncertainty over whether the ship asked for help, with the same official saying it “did not emit a distress call.”

At the moment, it’s still unclear who owns and operates the tanker. The Equasis maritime database shows the Riah’s last known owner as UAE-registered RIAH Shipping & Trading Inc., which appears to be based in Singapore.