The launcher believed to fire the missile that brought down the plane July 17, killing all 298 aboard, had a basic radar system unable to offer a complete view of all aircraft in the sky, the officials explained. Antiaircraft devices, such as the one that fired the SA-11 missile, typically work in tandem with other radar that offers the capability to distinguish between military and civilian aircraft.
With a lack of secondary radar images, those who fired the missile likely were not aware it was trained on a civilian aircraft, the officials said.
"It does appear to be a mistake," said one U.S. official, who added he was not authorized to speak publicly.
The information came as the black boxes, which recorded the in-flight actions of the plane, arrived at the Air Accidents Investigation Branch in Farnborough, England, for evaluation, and the bodies of 40 of the victims arrived to a somber ceremony Eindhoven, Netherlands. The plane was traveling from Amsterdam to Kuala Lumpur, Malaysia, when it crashed.
The U.S. officials confirmed that, since the accident, Russia has accelerated the delivery of military equipment to Ukraine. At least 20 tanks and armored vehicles entered eastern Ukraine Tuesday.
U.S. analysts have also confirmed the authenticity of audio recordings of conversations by separatists after the crash, and of photographs posted online showing a missile launcher heading toward the Russian border from Ukraine with one missile missing.