Here's the U.S. accusation against Russia:
STATE DEPARTMENT SPOKESPERSON MARIE HARF: "We have new evidence that ... Russia is firing artillery from within Russia to attack Ukrainian military positions." (Via MSNBC)
It's a big claim. If Russia is firing into Ukraine, that would be important for a couple reasons. It would essentially show Russia is — despite official statements to the contrary — providing escalating support for the uprising against the Ukrainian government.
Observers are citing this YouTube video as proof that Russia is firing into Ukraine, though no media outlet has been able to independently verify its authenticity.
The U.S. made its accusation public Thursday in a State Department media briefing.
Russia's state-owned RT posted the whole briefing to its YouTube channel and website, and skeptically titled it "State Dept. accuses Russia of firing artillery into Ukraine, refuses to provide any evidence."
And it's true that other than pointing to unnamed intelligence sources, the State Department didn't provide any further evidence of its claim — just that those intelligence sources were "highly confident." For its part, Russia denies the accusation.
The backdrop you can't ignore here is the downing of MH17 last week. Western officials have suggested Russia might have played a role in that attack, though an investigation into that is ongoing. (Via Getty Images)
Ukrainian officials also say two Ukrainian fighter jets were shot down earlier this week by Russia, though there's been no official evidence that that was the case either.