Tankers carrying Russian crude increasingly turned “dark” in June after the European Union agreed an import ban on the country’s oil and petroleum products, according to data platform Vortexa.

The number of tankers carrying Russian crude or products that turned off their AIS for more than 24 hours increased from 17 to 36 from May to June, it said.

The switch-offs included three suspected ship-to-ship (STS) transfers outside the Azores in the middle of the Atlantic Ocean — a new development in “dark” activity, according to London-based analyst Ioannis Papadimitriou.