"Who could have have shot this down? Who had the equipment — it's obviously an anti-aircraft missile? Who could have had the expertise to do that?" said Clinton, the likely Democratic presidential front-runner in 2016, said. "There does seem to be some growing awareness that it probably had to be Russian insurgents."

If pro-Russian separatists, who are battling the Ukrainian government, did indeed shoot down the plane, Clinton said the Russian government would be certainly linked to the crash.

"If there is evidence pointing in that direction, the equipment had to have come from Russia. What more the Russians may or may not have done, we don't know," she said.