Moscow denies any involvement in the disaster and has blamed the Ukrainian military. While stopping short of direct blame on Moscow, Kerry put forward the most detailed U.S. accusations so far, based on the latest U.S. intelligence assessments.

British Foreign Secretary Philip Hammond urged Moscow to ensure international investigators had access to the crash sites. "Russia risks becoming a pariah state if it does not behave properly," he told Sky television.

As Ukraine accused the rebels of hiding evidence relating to the loss of the airliner, a separatist leader said items thought to be the stricken jet's "black boxes" were now in rebel hands.

Investigators from the U.N. aviation agency arrived in Ukraine to help probe the crash, but a senior official said safety concerns prevented them from reaching the crash site.

"Until safe passage for them is assured, we don't send people into that kind of situation," said the official with the Montreal-based International Civil Aviation Organization.

Kerry said the United States had seen supplies moving into Ukraine from Russia in the last month, including a 150-vehicle convoy of armored personnel carriers, tanks and rocket launchers given to the separatists.

It had also intercepted conversations about the transfer to separatists of the Russian radar-guided SA-11 missile system, which it blames for the Boeing 777's destruction. "It's pretty clear that this is a system that was transferred from Russia," Kerry said in an interview on CNN.

"There's enormous amount of evidence, even more evidence that I just documented, that points to the involvement of Russia in providing these systems, training the people on them," he said on CBS. (rt/ez)