The US says it has identified at least six Panamanian-flagged tankers carrying Iranian crude this year as it put pressure on the registry to enforce its sanctions regime.

The US deputy special envoy for Iran, Abram Paley, urged Panama to end its association with tankers and operators trying to “abuse” the registry by hauling sanctioned oil.

Panama is the second-largest registry by gross tonnage worldwide, second only to Liberia, but it boasts a larger number of ships, totalling 8,321 vessels, according to Clarksons’ World Fleet Monitor.