PENTAGON: Russia Helped Whoever Shot Down The Plane

Pentagon spokesman Rear Admiral John Kirby said Friday that it "strains credulity" to think pro-Russian separatists in eastern Ukraine who are believed to have shot down Malaysia Airlines flight MH17 didn't have at least some help from Moscow.

"It strains credulity to think that they could do this without some measure of Russian support and assistance," Kirby said, in a briefing at the Pentagon.

Just 25 miles from Donetsk in pro-Russian held territory, the passenger flight carrying 298 passengers and crew was shot down on Thursday, killing everyone on board. The U.S. believes it was likely brought down by a SA-11 missile fired from a Buk surface-to-air missile system.

While he said more details would emerge in a deep investigation of the incident, Kirby noted the SA-11 is a "sophisticated piece of technology" that would likely require technical assistance from Russia.

In June, the U.S. State Department accused Russia of sending tanks and other heavy military equipment to the separatists in the east, including T-64 tanks and several rocket launchers.

Kirby continued:

"There have been Russian, I mean there have been incursions across the border by Russian aircraft. So, I mean we don't have any reason to suspect that they have not provided some measure of support on the other side of that order. These paramilitary forces that we do not talk about as much anymore certainly didn't act or behave or organize or resource like some ragtag militia. So nobody is suggesting that Russian military advice and assistance hasn't somehow crossed that border. It's just unclear exactly how much and when and who."

Shortly after the airliner had crashed, pro-Russian militants were reportedly caught on leaked phone calls, apparently discussing the shooting before eventually realizing they had shot down a civilian aircraft instead of a military target.

In one of the leaked calls, one militant asks, "What was it doing in Ukraine's territory?" Another, identified as Nikolay Kozitsin, responds, "That means they were carrying spies. F--- them, got it? ... They shouldn't be f---ing flying. There is a war going on."

Kirby also noted the continuous buildup of regular Russian army troops on the other side of the border, which he said now stands between 10,000 and 12,000 soldiers.

While much of the world is pointing the finger at Moscow's support for the insurgency in the east, Russian President Vladimir Putin has suggested the Ukrainian government is to blame.