Panama's president Juan Carlos Varela issued a decree that strips his country's flag from Iranian vessels, according to the US State Department.
The decree followed Washington's "exposure of an oil-for-terror network", according to an Iran 'Fact Sheet' issued by the department.
Panamanian authorities could not be reached for comment.
Panama's decision "to pull registration and de-flag Iranian vessels" comes after the state-owned National Iranian Tanker Company (NITC) fleet started reverting back to using their own national flag..
It is likely the entire NITC fleet is now once again using the Iranian flag, although some ambiguity remains because of increasingly patchy transponder data.
Flying the widely used Panamanian flag of convenience helped the Iranian tanker fleet to secure western insurance coverage and — for a time at least — to access European ports. When flying the Panamanian flag, NITC ships were subject to Panama's maritime laws, regulations, taxation and certification, as well as potential enforcement.
"Countries like Singapore, Sri Lanka and Sierra Leone have exercised great diligence to disrupt these schemes and deny criminal Iranian entities access to flag registries, insurance, and classification," according to US State Department special Iran envoy Brian Hook. This has further reduced Iran's potential options for alternative countries in which to register their ships.

