By Kristina Wong - 07/18/14 02:28 PM EDT
Pentagon officials on Friday said it “strains credulity” to believe that rebel forces in Ukraine could fire a surface-to-air missile and down a passenger jet without Russian help.
It “strains credulity that it [the missile system] could be used by separatists ... without some measure of Russian support and assistance," said Pentagon press secretary Rear Adm. John Kirby.
President Obama earlier Friday stopped short of directly charging that Russian separatists fired the missile, but his comments suggested U.S. intelligence is nearing that conclusion.
Kirby said the Pentagon had “very strong evidence” that a surface-to-air missile from an SA-11 Russian-built system was fired from separatist-controlled territory.
Pro-Russian militias in Ukraine have been fighting Kiev for greater autonomy following Moscow’s annexation by force of the Crimean region. Those forces are believed to have received significant military support from Russia, including tanks, armored personnel carriers, trucks and other "major equipment."
"There is no hint that Russian support for the separatists has ceased," said Kirby. "We believe that there is Russian support for the separatists inside Ukraine."
Kirby said the U.S. does not have evidence of a particular SA-11 system crossing the border from Russia but said such weapons transfers could easily have been hidden.
"We're not ruling anything in or out at this point," he said.
Gen. Philip Breedlove, NATO Supreme Allied Commander - Europe told Pentagon reporters several weeks ago that some of the separatists have received training from Russians on vehicle-borne anti-aircraft systems.
Kirby said he did not have any "great visibility" into who exactly downed two Ukrainian military planes earlier in the week.
"It's doing nothing to de-escalate the crisis in Ukraine," he continued.
Kirby also repeated U.S. calls for an immediate cease-fire between the separatists and Ukrainian forces to allow international investigators to safely access the crash site.
Kirby said the Pentagon doesn't know who has the plane's black box at this time, crucial evidence for investigators to determine what happened to the jet.
The Pentagon also said there was no sign that Russia was pulling back military forces amid the new crisis. Up to 12,000 Russian forces are still positioned by Ukraine's southeastern border and continue to grow "week by week," he said.
"They're very ready. It's a very capable force," he added.
The U.S. is continuing to provide nonlethal support to Ukrainian forces, including packaged meals, radios, body armor, first aid kits, sleeping mats, night vision goggles, Kevlar helmets and explosive detection devices.