The Iranian oil tanker Grace 1 in the Strait of Gibraltar this month. A five-week standoff between British and Iranian authorities over the possible violation of sanctions ended with the release of the ship

Russia has offered to help Iran to skirt US sanctions by allowing it to transport crude oil through ports in Crimea, in a further sign of growing ties between Moscow and Tehran.

Iran has previously sent oil deliveries to Syria and Turkey through the Suez Canal. That route has become problematic, according to Iran and Syria, since President Trump pulled out of a nuclear deal with Tehran and imposed economic sanctions.

Countries that purchase Iranian oil or assist its shipment risk US economic penalties. A tanker carrying Iranian oil to Syria was detained last month by the Egyptian authorities as it travelled through the Suez Canal, according to Iranian state media. Cairo denied the reports and insisted that the waterway remained open to Iranian vessels.