Four Hong Kong companies have landed on the US sanctions blacklist for allegedly helping Islamic Republic of Iran Shipping Lines (IRISL) to buy a containership.

Delight Shipping, Gracious Shipping, Noble Shipping and Supreme Shipping — all based out of the same Hong Kong address in Sheung Wan — were sanctioned by the US Department of State on Monday after appearing to help the Iranian shipowner take control of the 14,508-teu Hamouna (built 2018).

The US Treasury's Office of Foreign Asset Control has added the companies to its Specially Designated Nationals list.

"Today, we reiterate a warning to stakeholders worldwide: If you do business with IRISL, you risk US sanctions," secretary of state Mike Pompeo said.

US authorities provided few details on the sale, but VesselsValue data shows the Hamouna, then known as Canreach, assumed sold by Reach Shipping Lines to an Iranian company named Rahbaran Omid Darya in January for an undisclosed price.

The Hamouna was one of the IRISL-connected vessels blacklisted in June when the Tehran-based shipowner and its Shanghai subsidiary E-Sail Shipping were sanctioned after a 180-day wind-down period the US afforded the company's customers.

The Hamouna's registered owner was Noble Shipping until February and was flagged in Comoros until January, when it was re-flagged in Iran, according to shipping databases.

Its current registered owner, Oghyanous Khoroshan Kish, shares an address with Rahbaran Omid Darya. Both were previously sanctioned.

It is unclear how Delight Shipping, Gracious Shipping and Supreme Shipping were involved.

The Hamouna has a market value of $129m, according to VesselsValue.

Reach Shipping Lines was also blacklisted in this round of sanctions, though the State Department only accused it of helping IRISL, E-Sail and a third subsidiary, Hafez Darya Arya Shipping, evade US sanctions.

The State Department said Reach provided services to the trio to help conceal their activities from the Chinese government and maritime stakeholders, lied to other Chinese companies to cover up Iranian involvement and falsified documents.

In addition, Reach Holding Group was sanctioned, along with chief executive Eric Chen and president Daniel He.

The recent actions are the latest in the US "maximum pressure" campaign against Iran, which began in 2018 when it dropped out of a deal that saw Tehran agree to curtail its nuclear programme in exchange for the lifting of sanctions.

Since then, the US has steadily sanctioned shipping companies for doing business with Iran and Venezuela, which have begun more readily trading with each other.

The crackdown has sent many of shipping's more scrupulous outfits scrambling to build compliance systems, with some arguing it is impossible to do so.