Sky News correspondent Mark White, citing aviation sources, said the aircraft appeared to have been flying through a block of airspace deemed "not suitable for civilian aircraft".
"It raises questions about why the plane was in an area it had been advised not to fly through.
Sky's Katie Stallard, in Moscow, said media reports suggest the plane came down in an area where there has been recent heavy fighting amid continuing tensions between Russia and Ukraine.
Data from Flightradar24 indicates the plane had just passed the city of Kremenchuk, around 300km (186 miles) from the Russian border, when it disappeared.
Aviation expert Major Charles Hayman told Sky News: "It's highly likely this aircraft was flying along a fault line between Russian and Ukrainian defences.
"It's possible the Ukrainians flapped a bit, thought it was hostile and shot it down.
"It looks like someone failed to recognise this was a civilian plane."
