"The matter is being examined," IOC said in response to a Reuters email seeking comment after the U.S. Treasury Department on Wednesday imposed sanctions on five Chinese nationals and six entities it said had violated Washington's unilateral curbs on Tehran.

These included two Cosco Shipping Corporation subsidiaries, Cosco Shipping Tanker Dalian and Cosco Shipping Tanker (Dalian) Seaman and Ship Management Co.

IOC has chartered Da Yuan Hu, owned by Cosco Shipping Tanker Dalian, for the lifting of 145,000 tonnes of Mexican Isthumus oil. The vessel is expected to start its voyage to Paradip port in eastern India on Oct. 10, Refinitiv Eikon data shows.

No response was available from Nayara Energy over its charter of a vessel linked to Cosco Shipping. Nayara is partly owned by Russian oil major Rosneft.

Refinitiv Eikon data showed that Nayara has chartered Da Ming Hu to lift oil from the U.S. Gulf coast on Oct. 6.

(Reporting by Nidhi Verma in NEW DELHI and Chen Aizhu in SINGAPORE; Editing by David Goodman)