"Russia is supporting these separatists. Russia is arming these separatists. Russia is training these separatists, and Russia has not yet done the things necessary in order to try to bring them under control," he said.
In a round of television interviews, Kerry cited a mix of U.S. and Ukrainian intelligence and social media reports that he said "obviously points a very clear finger at the separatists" for firing the missile that brought the plane down, killing nearly 300 passengers and crew.
"It's pretty clear that this is a system that was transferred from Russia into the hands of separatists," he said.
Video of an SA-11 launcher, with one of its missiles missing and leaving the likely launch site, has been authenticated, he said.
An Associated Press journalist saw a missile launcher in rebel-held territory close to the crash site just hours before the plane was brought down Thursday.
"There's a buildup of extraordinary circumstantial evidence," Kerry said. "We picked up the imagery of this launch. We know the trajectory. We know where it came from. We know the timing, and it was exactly at the time that this aircraft disappeared from the radar. We also know from voice identification that the separatists were bragging about shooting it down afterward."
In one set of calls, said by Ukrainian security services to have been recorded shortly after the plane was hit, a prominent rebel commander, Igor Bezler, tells a Russian military intelligence officer that rebel forces shot down a plane.
Shortly before Kerry's television appearances, the U.S. Embassy in Kiev, the Ukrainian capital, released a statement saying experts had authenticated the calls.
"Audio data provided to the press by the Ukrainian security service was evaluated by intelligence community analysts who confirmed these were authentic conversations between known separatist leaders, based on comparing the Ukraine-released internet audio to recordings of known separatists," the statement said.
A new set of recordings apparently made Friday also appears to implicate rebels in an attempted cover-up at the crash site.
In one exchange, a man identified as the leader of the rebel Vostok Battalion Alexander Khodakovsky states that two recording devices are being held by the head of intelligence of the insurgency's military commander. The commander is then heard to order the militiaman to ensure no outsiders, including an international observation team near the crash site at the reported time of the call, get hold of any material.
The man identified as Khodakovsky says he is pursuing inquiries about the black boxes under instructions from "our high-placed friends ... in Moscow."
In another conversation with a rebel representative at the crash site who reports finding an orange box marked as a satellite navigation box, Khodakovsky is purported to order that the object be hidden.
U.S. aviation safety experts say they are especially concerned the site will be "spoiled" if it cannot be quickly secured by investigators. Based on photographs, they say it is a very large debris field consistent with an in-flight explosion and the main evidence to be collected would be pieces of the missile.
Because the integrity of the plane and actions of the pilots are not an issue, the experts do not believe the flight recorders will yield much useful information.