Rebel groups in eastern Ukraine said to have been shooting at planes and helicopters with Buk missiles over past week

The Malaysia Airlines plane that crashed over Ukraine on Thursday, killing all 283 passengers and 15 crew, may have been shot down by a vehicle-mounted Russian-built Buk missile system, according to western-based defence specialists.

Russian-backed rebel groups or Russian forces based in eastern Ukraine are said to have been shooting at planes and helicopters with Buk missiles over the last week in an attempt to achieve mastery of the airspace.

But Russian fighter planes have also been in action this week, allegedly responsible for downing a Ukrainian jet. It is easier for aircraft to accurately target planes but it should also be easier for a pilot to identify a plane as a commercial airliner.

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 Ukrainian interior minister Anton Gerashenko has blamed for the attack, has a range of up to 25,000 metres.

Pentagon spokesman Rear Admiral John Kirby said that the 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 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 experts. Russia is alleged to have infiltrated special forces into Ukraine in the guise of rebels.

Sutyagin, who monitors social media in Ukraine, said a Ukrainian rebel force had been spotted just hours earlier with a Buk system 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 missile, codenamed "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. Ukrainian forces also use it.

The Ukrainian government has been making headway against rebel forces recently and Russia has adopted a strategy of denying airspace to its jets, restricting it to the use of troops on the ground.

In a series of incidents over the last week, a Ukrainian Sukhoi Su-25 jet was shot down by an air-to-air missile on Wednesday evening. Pro-Russian rebels claimed they had downed a second Su-25 the same day; Ukrainian defence force said it had been hit by a ground-launched missile. On Monday, a Ukrainian military transport was hit by a missile supposedly from Russia; the plane was beyond the range of a MANPAD.

On Thursday, an Associated Press reporter reported seeing a Buk in the east Ukrainian town of Snizhne.

Pro-Russian rebels the Donetsk People's Republic have taken control of a military base with Buk systems. But they are useless without specialist knowledge. 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 requires knowledge of how to use radar, how to lock on to a target and a host of other steps beyond the average rebel.

"If the plane was shot down, it could only have been shot down by a state authority," Eyal said, suggesting 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 said. "The only country that has a persistent policy of trying to prevent Ukrainians controlling airspace is Russia. Russia has taken an interest in shooting down aircraft and forcing Ukraine to use ground troops."

The Buk was used by both sides in the Russian-Georgia war in 2008, with Georgia using it to down four Russian aircraft.