John Kerry has said the US has "overwhelming evidence" of Russian complicity in the downing of a Malaysian airliner in eastern Ukraine.
In a series of interviews on Sunday, the US secretary of state demanded that Russia take responsibility for the actions of pro-Russian rebels suspected of shooting down MH17 on Thursday, killing 298 people.
Kerry said that US spies had intercepted conversations about the transfer to separatists of the Russian radar-guided SA-11 missile system it blames for the plane downing.
The US also had a video of a missile launcher - with at least one rocket missing from its battery - moving back into Russia from a rebel-held area, Kerry said.
"There's [an] enormous amount of evidence, even more evidence than I just documented, that points to the involvement of Russia in providing these systems, training the people on them," Kerry said on the CBS news network.
He said the US had evidence of a 150-vehicle convoy of armoured vehicles, tanks and rocket launchers transferred from Russia to the separatists several weeks ago. None of the evidence was released to the public.
"It is clear that Russia supports the separatists, supplies the separatists, encourages the separatists, trains the separatists. And Russia needs to step up and make a difference here," Kerry said on the NBC news network.
Kerry expressed disgust over the rebels' mishandling of victims' bodies.
"Drunken separatists have been piling bodies into trucks and removing them from the site... What's happening is really grotesque and it is contrary to everything ... Russia said they would do."
Moscow denies involvement and has accused the Ukrainian military of causing the disaster.
A separate intelligence report, published at the weekend, said the US had confirmed that a recording released by the Ukraine government of separatists boasting of shooting down the plane, was authentic.
It also stated that US spies had information that Russia is providing training to separatists in southwestern Russia on missile systems.
Kerry told Fox News that the US was "prepared to take additional steps" against Russia.
"We are discussing with the Ukrainians right now what they need, what else we can do," he said, adding all options were "on the table" - except sending in US troops.