The Defence Secretary says it is "clear" explosions at a Russian air base in Crimea were not caused by "someone dropping a cigarette", as he dismissed Moscow's "excuses" for the blasts.
There is speculation that the explosions at Saky Air Base, which killed one person and left several others wounded, were the result of a Ukrainian attack.
Ben Wallace believes anyone’s "manual of war" would deem the site on the Crimean Peninsula a "legitimate target" for Ukraine to try and hit.
Ukraine's air force claims nine Russian jets were destroyed in Tuesday's blasts, but the country's officials have not claimed responsibility.
Moscow has denied any aircraft were damaged, or that an attack took place.
Mr Wallace said it was "very early days" and the UK would "see what information comes out" about the incident at the Saki air base.
He told the BBC: "We've pretty much dismissed most of the Russian, I think, excuses – everything from a cigarette butt, I think was one of them, that might have set off two simultaneous large explosions.
"I think when you just look at the footage of two simultaneous explosions not quite next to each other, and some of the reported damage even by the Russian authorities, I think it’s clear that that’s not something that happens by someone dropping a cigarette."
Russia's state news agency Tass cited an unnamed defence ministry source as saying the key cause of the blasts seemed to be "violations of fire safety rules".