10:31 GMT
Joshua Cheetham
BBC Verify journalist
We’ve examined satellite imagery of Novorossiysk, where Ukraine says it carried out an undersea drone attack on a Russian submarine on Monday.
Imagery from 11 December, days before the attack, shows three submarines docked inside a quay, surrounded by several warships.
Another picture taken on 16 December shows only one submarine in the quay’s interior, next to an area of heavy damage.
A second submarine is seen along the exterior quay wall, and a third is docked farther south on another pier which is not visible in the composite above. It’s unclear whether these two are the same submarines previously seen inside the quay.
Bradley Martin, a senior policy researcher at Rand, says the submarine pictured inside the quay on 16 December is the one allegedly hit.
He believes it’s sitting lower in the water, which may suggest some kind of damage. However, he says the pictures are inconclusive and so is the video of the explosion released by Ukraine.
“Submarines are intended to operate at depth and endure explosive shocks,” Martin adds. “An explosion next to the submarine would look spectacular, but we’d need to know a lot more before concluding that the sub is sunk or even severely damaged.”