On Monday, the HUR reported that the Sparta had broken down off Portugal, but the problem had been fixed. Ursa Major was originally known as Sparta III, so it was not clear which ship the Ukrainians were referring to.

However, the Sparta also got into difficulty a week ago, in rough seas off Brittany in the north-west of France. Radio France Inter reported that the Russian cargo ship initially did not respond to French communications on Tuesday 17 December, until acknowledging it had a problem.

“I’m in trouble. My engines are currently down, the tiller isn’t responding. We’re going to try to repair it in the coming minutes,” RFI reported the ship’s radio as saying, external.

After drifting for 61 minutes, the Sparta said it was back on course.

It is not known what caused the explosion on Ursa Major as it passed between Oran in Algeria and the Spanish town of Águilas on Monday afternoon.

However, video filmed from the tanker Ross Sea between 12:00-13:00GMT on 23 December, and verified by the BBC, showed the ship listing badly.

It eventually sank at about 01:20GMT on Tuesday.

Ursa Major was built in 2009 and placed under sanction after Russia’s full-scale invasion in Ukraine in 2022 because of the ship owner’s role in delivering cargo to the Russian military.

Oboronlogistika said the cargo ship, which it described as the flagship of its fleet, was carrying 45-tonne hatch covers for icebreakers, as well as the large cranes for the port in Vladivostok.

Additional reporting by BBC Verify’s Josh Cheetham, Paul Brown and Daniele Palumbo