A Russian-made surface-to-air missile is the most likely cause of the suspected downing of a Malaysian airliner over Ukraine, analysts said on Friday, as claim and counter-claim swirled over who launched the weapon.

The truck-mounted "Buk" missile is capable of soaring to the height of a civilian airliner like Malaysian Airlines flight MH17, unlike lighter and more widely available shoulder-launched weapons, defence experts said.

Developed by the Soviet Union in the 1970s to shoot down aircraft, helicopters, cruise missiles and drones, it is still widely used by both the Ukrainian and Russian militaries.

But pro-Russian rebels in eastern Ukraine had just hours before the disaster announced that they had seized a number of Buks themselves.

"Who has shot it down? There is lots of evidence which shows these were pro-Russian separatists who have done that," Russian defence expert Igor Sutyagin of the Royal United Services Institute (RUSI) told AFP.

He cited a Twitter post on Thursday by separatists, later deleted, "when they reported that they had captured precisely that piece of hardware known as Buk".

The radar-guided missile can hit targets flying as high as 72,000 feet (22 kilometres) -- more than twice the 33,000 feet MH17 was cruising at -- and have a range of 32km, said IHS Jane's Missiles and Rockets editor Doug Richardson.

The missiles travel at three times the speed of sound and have an explosive warhead weighing 70 kilograms (154 pounds).

There are two variants: the Buk-M1 and Buk M2, codenamed by NATO as the SA-11 Gadfly and the SA-17 Grizzly.

The US envoy to the United Nations, Samantha Power, said on Friday it was likely that an SA-11 was responsible.

The missile is produced by the Russian arms firm Almaz-Antey, recently targeted by US sanctions, at a factory in Ulyanovsk.

- Warning of an airliner -

Richardson said the missile system has a "friend or foe" identification system, but could not distinguish a commercial airliner from another unknown plane.

"It would not give you a warning that you were tracking an airliner," he said.

Buk missiles are complicated to operate, requiring three lorry-sized vehicles -- a command post, a radar vehicle, and a launcher with the missiles -- which suggests that some expertise was needed to operate them, analysts said.

Ukraine pointed the finger at separatist rebels, who -- if responsible -- could have either captured the missile from Ukrainian forces or have had it supplied by Russia, experts say.

Two Ukrainian military planes were shot down in the weeks before the Malaysian Airlines jet crashed.

A message on the official Twitter account of rebel group the Donetsk People's Republic said on Thursday that insurgents had seized a series of Buk systems from a Ukrainian surface-to-air missile regiment.

Hours later, the group's "defence minster" Igor Strelkov on his local social networking page claimed to have downed what they said was a Ukrainian military transport plane. Both messages were later deleted.

Eliot Higgins, who posts detailed analyses of weapons in Syria and other conflicts on his Brown Moses blog, said he had traced a video of a Buk missile launcher about 12 kilometres (7.5 miles) from the crash site.

"The video was uploaded on July 17th. I've found no other versions of it, and it was on a new YouTube account which was deleted a few hours later," he said in an email to AFP.

The launcher was "heading out of an opposition-controlled town, close to the town centre, heading south, which is towards the Russian border", he said.

Jonathan Eyal, International Director at RUSI, said it was "impossible to believe" rebels could have hit their target without radar and other logistical support from the Russian military.

But Russia's defence ministry said Friday that a Ukrainian Buk radar was operating on the day of the crash.