A U.S. official confirmed to The Washington Post on Saturday that Russia supplied advanced missile launchers to separatist groups in Ukraine, and that those launchers were moved back across the border after the downing of Malaysia Air Flight 17. The Russian government has so far denied sending weapons to the rebel groups, and the rebels have denied possessing them, though they have boasted online about shooting down other aircraft.

According to the report by journalists Michael Birnbaum and Karen DeYoung, U.S. intelligence officials learned "a little more than a week ago" that Russia was attempting to move the weapon systems, known as the Buk-M1, into Ukraine. Several videos have surfaced over the last two days of the mobile launchers being moved on Ukrainian roads, including back toward the Russian border, though those videos were unconfirmed. This would appear to be the first direct accusation from American sources tying the disaster to the Russian government.

Although Ukraine has their own versions of the Russian-made Buk missiles, the government claims they did not leave any behind in separatist controlled-areas. If true, the missiles could likely have only come from the other side of the Russian border.

Earlier on Saturday, the Ukrainian government announced it had evidence directly tying the Russians to the crash. The head of Kiev's state security service, Vitaly Nayda, displayed pictures of Buk missiles being moved toward the Russian border.

Meanwhile, officials from several countries who lost citizens in the crash are growing increasingly frustrated with the inability to secure the crash site for a proper investigation, and to recover the bodies of the victims. Journalists on the scene report that armed separatists, some of whom were visibly drunk, denied foreign investigators access to the site on Saturday. There are also a number of reports that the bodies of some of the victims have been taken away to unknown locations, possibly to hide or destroy evidence. Those that remain are quickly decomposing in the heat and humidity, and much of their personal property has been looted.

Dutch Prime Minister Mark Rutte is reportedly "furious" with Russian President Vladimir Putin, with whom he had a tense and "personal" phone conversation on Saturday. "I told him 'time is running out for you to show the world that you have good intentions, that you will take responsibility,'" Rutte said. At least 193 of the 298 people on board the plane were from the Netherlands. Australian Prime Minister Tony Abbott (who lost 28 of his own citizens) has essentially accused Russia of being complicit in the attack and threatened to withhold Putin's invitation to the G20 summit in November.