Two oil tankers allegedly part of Russia‘s “shadow fleet” that were sailing off Turkey’s Black Sea coast may have been struck by mines, drones, or missile, a Turkish official said.

Fires broke out on both vessels, the Kairos and the Virat, in quick succession on Friday. The Kairos caught fire in the Black Sea some 28 nautical miles off the coast of the country’s Kocaeli province, according to Turkey’s Directorate General of Maritime Affairs. The vessel was travelling without cargo towards Russia’s Novorossiysk port when the blaze began, the Directorate General of Maritime Affairs said.

Within an hour, a second tanker, Virat, was “struck” while sailing in the Black Sea around 35 nautical miles off the Turkish coast, the maritime authority reported.

Turkish Transport and Infrastructure Minister Abdulkadir Uraloglu said rescue crews first received reports that the Kairos may have struck a mine before being informed that an explosion had occurred on the Virat, the Associated Press reports.

Mr Uraloglu suggested the cause of the two incidents isn’t yet clear. Speaking to broadcaster NTV on Saturday, he said: “Our crews indicate that there were explosions on the other ship and that these were also caused by external interference.”

He said the “first things that come to mind for external interference could be a mine, a missile, a marine vessel or a drone”, but they “don’t have definitive information on this”.

All 25 crew aboard the Kairos, a Gambian-flagged tanker, were evacuated to safety, authorities said. The 20-person crew on the Virat were also safe, although it was reported that there had been heavy smoke in the engine room, according to the maritime authority.

OpenSanctions, which describes itself as a “comprehensive database that consolidates sanctions lists, government watchlists, lists of politically exposed persons (PEPs), entities involved in financial crime, and parties excluded from government contracts” claims the two ships are part of a shadow fleet used to evade sanctions imposed on Russia in the wake of its full-scale invasion of Ukraine in 2022.

According to the website, the Virat was sanctioned by the US in January this year. It was subsequently sanctioned by the European Union, Switzerland, the United Kingdom and Canada.

Meanwhile, the EU sanctioned the Kairos in July this year, followed by the UK and Switzerland.

The GUR, Ukraine’s military intelligence service, claims on its website both vessels visit Russian ports and have a history of shutting off their automatic identification systems, which are used to transmit a ship’s position.

They have also docked at ports in China, Turkey and India, and elsewhere.