A Malaysian airliner with 298 people on board was shot down over Ukraine by a surface-to-air missile Thursday but it was unclear who fired the weapon, US officials said.
Intelligence analysts are reviewing data from a military satellite and other sources to determine whether the missile was launched by pro-Moscow separatists in Ukraine, Russian troops across the border or Ukrainian government forces, two US officials told AFP on condition of anonymity.
"We are working through all the analysis," said one official.
But there was little doubt that the plane was struck by a surface-to-air missile.
"That's what we strongly believe," the official said.
At an event in Detroit, Vice President Joe Biden said the US-made Boeing 777 was intentionally "blown out of the sky."
The aircraft was "apparently... and I say apparently because we don't have all the details yet... shot down. Not an accident. Blown out of the sky," Biden said.
Soon after the plane went down, Ukrainian leaders accused pro-Russian separatists of bringing down the airliner in a "terrorist" attack.
Speculation has focused on the possibility that the airliner was shot down inadvertently, possibly by pro-Russian forces believing they were targeting a Ukrainian army transport plane.
The aircraft was reportedly flying at an altitude of more than 30,000 feet (10 kilometers), putting it well within range of Russian-made Buk missiles that are in the arsenals of both Ukrainian and Russian forces.
Widely used, the Buk surface-to-air missiles are mobile systems installed on wheeled or tracked vehicles and are designed to strike aircraft, cruise missiles, helicopters and other targets.
Before the conflict in Ukraine began, Kiev government forces had about six to eight batteries of the missile, according to military analysts.
Russia has many more at its disposal, as well as more sophisticated missiles, though it remains unclear if they are deployed near Ukraine.
- Friend or foe system -
Buk missiles are complicated to operate, unlike shoulder-launched weapons, and it would require outside help or extensive training for pro-Moscow separatists in Ukraine to be operating the missile batteries, said IHS Jane's senior defense analyst Edward Hunt.
"They're normally not seen within insurgent or separatist forces for the very reason they're quite manpower intensive, training intensive and spare parts intensive," Hunt said.
Buk weapons require several people to operate, including a radar operator coordinating with those launching the missiles from a common post vehicle.
They have a "friend or foe" identification system but can't distinguish a commercial airliner from another unknown plane, according to analysts.
"It is the electronic equivalent of a sentry calling out 'Who goes there?,'" said IHS Jane's Missiles & Rockets editor Doug Richardson.
"If there is no reply, all you know is that it is not one of your own side's combat aircraft. It would not give you a warning that you were tracking an airliner,"
Ukrainian air traffic controllers lost contact with Malaysian Airlines flight MH17 at 1415 GMT, about four hours into its flight and some 30 miles (50 kilometers) from the Russia-Ukraine border.
The plane had taken off from Amsterdam en route to Kuala Lumpur.
There were no signs of survivors at the crash site in eastern Ukraine, where there were horrific scenes of carnage. (AFP)