Shoulder-held MANPAD missiles are popular with guerrilla groups worldwide but the Malaysian Airlines plane would have been flying above 10,000 metres, well beyond their range. The Buk, which the Ukrainian interior minister, Anton Gerashenko, blamed for the attack, has a range of 22,000 metres.
Pentagon spokesman Rear Admiral John Kirby said US secretary of defence, Chuck Hagel, had been briefed on the crash, but Kirby was unable to confirm details of what happened or what the US knew.
Nato surveillance planes policing the Baltic states were unable to identify the source of the attack.
Igor Sutyagin, a Russian military specialist at the London-based Royal United Services Institute, said that he believed that either Russians or Russian supported groups in eastern Ukraine were responsible. He said they had been shooting at Ukrainian aircraft over the last week.
Kalashnikov-carrying Russian sympathisers in Ukraine would not have had the expertise to use the Buk system and would have needed either specialists who had "volunteered" their services from Russia or locally-recruited specialists. Russia is alleged to have infiltrated special forces into Ukraine under the guise of being rebels.
Sutyagin, who monitors social media in the Ukraine, said a Ukrainian rebel force had been spotted just hours earlier with a Buk at Torez, a village close to the site where the plane came down.
He added that a Ukrainian transport plane had been flying overhead close to the time that the missile was fired at the Malaysia Airlines plane, suggesting that may have been the original target. The transport plane had been trying to relieve a beleaguered Ukraine garrison.
The Buk, dubbed "Grizzly" by Nato, was developed by the USSR in the 1970s to shoot down cruise and other missiles. It has since gone through many redesigns and upgrades, and been widely exported. Ukraine forces also use Buk.
Ukrainian forces have been making headway against rebel forces recently and Russia has adopted a strategy of denying them air space, forcing them instead to restrict them to the use of troops on the ground.
The Russian government, pro-Russian forces and the Ukrainian government were all shifting the blame for the shooting down of the Malaysia Airlines plane. But most of the recent incidents of planes being shot down have allegedly been the result of fire from either Russia or pro-Russian rebels.
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Jonathan Eyal, director of the Royal United Services Institute, said it was not a matter of climbing aboard a van and pressing a button. Firing a missile required knowledge of how to use radar, how to lock onto a target and a host of other steps beyond the average Kalashnikov carrying rebel.
"If the plane was shot down, it could only have been shot down by a state authority," Eyal said, adding either Russia or Ukraine, or by a group in Ukraine helped by Russia. On balance, he said he thought the blame rested with Russia.
The Buk, he said, "definitely has the range and is mobile and could be fired by Russians or Russian separatists. It amounts to a massive, massive escalation".
Eyal added: "The only country that has a persistent policy of trying to prevent Ukrainians controlling air space is Russia. Russia has taken an interest in shooting down aircraft and forcing Ukraine to use ground troops."