Countries targeted by tougher US sanctions, such as Iran and Venezuela, have responded with elaborate strategies to circumvent restrictions on their oil exports.
Top oil shipping companies say they have responded by tightening guidelines and deploying technology to prevent accidental sanctions violations, which U.S. officials say could result in them being cut off from the dollar financial system and having their assets seized.
Several shipping sources involved in legal advisory and insurance services to the industry told Reuters that inadvertent breaches are also becoming a growing risk for ship certification societies such as the American Bureau of Shipping (ABS), which withdrew cover for the two tankers earlier this month.
"Classification societies face the challenge of staying on top of Iran's tactics in order to avoid sanctions themselves," said Claire Jungman, chief of staff at United Against Nuclear Iran (UANI).
Classification societies provide services such as ensuring the seaworthiness of ships.
UANI, a U.S.-based group that monitors Iran-related tanker traffic through ship and satellite tracking, alerted ABS in December to what it said were Iranian oil transfers involving several vessels, including the Panama-flagged Karo and the Belize-flagged Elsa, according to correspondence seen by Reuters.
Reuters was unable to locate the owners of the two tankers' email addresses or phone numbers.
Iran considers US sanctions to be illegal and has stated that it will make every effort to avoid them. "There is a strong will in Iran to increase oil exports despite the unjust and illegal US sanctions," Iran's oil minister Javad Owji said on state television in September, without elaborating on how Tehran planned to circumvent the sanctions. more info
Iranian officials, who do not reveal details about their efforts to circumvent sanctions, did not respond to a phone call or an email request for comment from Reuters on Friday, which is the Iranian weekend.
ABS is the only American company among the top 12 ship classification societies, which are based in Europe and Asia and are critical to the operation of thousands of vessels in the global shipping fleet.
Vessels without certification are unable to obtain insurance or call at most international ports.
According to the ABS website, so-called class cover, which includes vessel safety inspections, was withdrawn for a ship named the Elsa on December 17, with sanctions cited as the reason, while cover for a second ship, the Karo, was withdrawn on January 13, with sanctions cited as the reason. There were no further details provided.
According to an ABS spokesperson, the company "strictly follows US sanctions law and takes seriously and investigates all claims and information received that may suggest that any vessel in ABS class is trading with a sanctioned country."
"In the event that the information is confirmed, ABS has cancelled and will cancel the involved vessel's ABS class in accordance with our policies and procedures," the spokesperson said, declining to comment on specific cases.
ABS stated in a Dec. 21 letter to UANI, seen by Reuters, that after conducting an independent investigation, it had discovered "material evidence" that the Elsa had "engaged in illicit transshipment operations with an Iranian tanker" on or about Dec. 8, and had thus cancelled all classification services.
ABS stated in a separate letter dated January 14 that it had completed a separate independent investigation of the Karo and had also cancelled all certification services associated with it.
According to the Equasis public database, which aims to provide transparency in shipping by publishing maritime data, Hong Kong-based Delta Lines is listed as the owner of the Elsa, which is its only ship.
Delta Lines is listed in a corporate registry office in Hong Kong, but when contacted by Reuters on Thursday, staff there were unable to provide any information about the company.
Karo Shipping Services, based in India, is listed as the owner of the Karo, the company's sole vessel, according to Equasis data.
When Reuters visited an office near Mumbai listed in shipping databases as the contact address for Karo Shipping Services on Tuesday, it was closed.
According to Eikon ship tracking data, the Elsa's last reported position was off the coast of Singapore on January 20, while the Karo's last reported position was off the coast of Taiwan on January 18.