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(CNN) – Following on the heels of the shoot down of Malaysia Airlines Flight 17, two Ukrainian military jets were shot down Wednesday in the eastern part of the country, where pro-Russian rebels have fought against government forces, a Ukrainian military office said.
The Ukrainian government says missiles fired from Russian territory brought them down.
The U.S. has not confirmed the details of what happened, the U.S. Ambassador to Ukraine tells CNN.
"But if it is confirmed, it reflects an outrageous, continued escalation of the crisis by Russia, even after the SA-11 (surface-to-air missile system) brought down an airplane leading to the death of nearly 300 innocent people," Ambassador Geoffrey Pyatt said in an interview with CNN's "The Lead with Jake Tapper."
U.S. officials say pro-Russian rebels were responsible for shooting down Flight MH17, but they say the rebels probably didn't know they were targeting a commercial airliner.
Less clear is who was ultimately responsible for the jet's destruction. Rebels blame Ukraine, Ukraine blames both rebels and Russia, and Russia points the finger back at Ukraine's military.
"There's very clear evidence about all aspects of this missile attack, with the sole question of who pressed the button," said Pyatt.
As for the missiles that took down Ukrainian military planes today, whether they came from Russia, or from eastern Ukraine where pro-Russian rebels are operating, doesn't really matter, says the ambassador.
"Russia has engaged in this pattern of destabilizing action, which began about two weeks ago to take a much more alarming turn, as we began to see heavy weaponry, large tank columns, armored personnel carriers flowing into Ukraine," said Pyatt.
Russia has "had its fingerprint on this crisis" since February when it annexed the Crimean Peninsula, and "this pattern has unfortunately only escalated for the past five months, reaching this tragic culmination on Thursday afternoon, when the Malaysia Airlines flight was brought down," Pyatt said.