Separatists have been quoted in Russian media saying they had acquired one. One group was quoted as saying that it used an SA-11 on Monday to bring down an Antonov An-26 turboprop plane - a loss that the Ukrainian forces had confirmed this week along with the downing of a Sukhoi Su-25 fighter on Wednesday.

An emergency worker said at least 100 bodies had been found so far and that debris was spread over 15 km (9 miles). People were scouring the area for the black box flight recorders and separatists were later quoted as saying they had found one.

Kiev complained that separatists who are the main force in the area prevented Ukrainian officials from reaching the site.

Malaysian Prime Minister Najib Razak demanded swift justice for those responsible and said the crash site must not be interfered with before international experts had access.

"MH-17 is not an incident or catastrophe, it is a terrorist attack," Ukrainian President Petro Poroshenko tweeted. He has stepped up his military campaign against the rebels since a ceasefire late last month failed to produce any negotiations.

One rebel leader, the self-styled prime minister in Donetsk, said they could agree a truce of two or three days to help with investigation of the incident.

Ukrainian Interior Ministry official Anton Gerashchenko said on Facebook: "Just now, over Torez, terrorists using a Buk anti-aircraft system kindly given to them by Putin have shot down a civilian airliner flying from Amsterdam to Kuala Lumpur."

The Buk - which means beech tree in Russia - is a 1970s vintage, truck-mounted, radar-guided missile system, codenamed SA-11 Gadfly by Cold War NATO adversaries. It fires a 5.7-meter, 55-kg missile for up to 28 km.

"There is no limit to the cynicism of Putin and his terrorists!" Gerashchenko wrote on the social media site. "Europe, USA, Canada, the civilized world, open your eyes! Help us in any way you can! This is a war of good against evil!"

He also published a photograph he said showed a Buk launcher in the centre of the town of Torez on Thursday. It was not possible to verify the image. On June 29, Russia's Itar-Tass news agency quoted a separatist spokesman in Donetsk as saying they had taken control of a Buk air-defense system.

The military commander of the rebels, a Russian named Igor Strelkov, had written on his social media page at 1337 GMT, that his forces had brought down an Antonov An-26 in the same area. It is a turboprop transport plane of a type used by Ukraine's forces. There was no comment on that from Ukrainian officials.

Flight MH-17 could have been in that area around that time, just over three hours after it took off from Schipol airport.

Several Ukrainian planes and helicopters have been shot down in four months of fighting in the region. Ukraine had said an An-26 was shot down on Monday and one of its Sukhoi Su-25 fighters was downed on Wednesday by an air-to-air missile - Kiev's strongest accusation yet of direct Russian involvement, since the rebels do not appear to have access to aircraft.

Moscow has denied its forces are involved in any way. (rt/ez)