Dutch-led air crash investigators Tuesday release their final report into the downing of Malaysia Airlines flight MH17 over war-torn Ukraine, in a move likely to worsen already-strained ties between Russia and the West.

As Dutch Safety Board officials prepared to unveil the highly anticipated findings of a 15-month inquiry, Moscow was gearing up to go on the counter-offensive after vehemently denying any role in the air disaster.

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The report, due to be released at 1115 GMT at the Gilze-Rijen air force base in southern Netherlands, is expected to say how the Boeing 777 was blown from the sky on July 17, 2014, but not who was responsible.

All 298 people on board, most of them Dutch and among them 15 crew members, were killed when the routine flight between Amsterdam and Kuala Lumpur was brought down -- possibly by a missile -- over eastern Ukraine.

The disaster happened during heavy fighting between Ukrainian forces and pro-Russian separatists, and Kiev and the West have squarely blamed the rebels.

Analyst Peter Felstead of Jane's Defence Weekly told AFP the airliner was most likely shot down "by mistake" by a BUK missile crew, who crossed the border to help the rebels counter Ukrainian air threats.

"We are expecting the report to confirm what we have assumed in that this was a Russian mistake," Felstead told AFP.

Either other Russians in the area, or local rebel commanders, "thought they had targeted a military aircraft in the area and it turned out to be an airliner," he added.

But both Moscow and state-owned arms maker Almaz-Antey deny the claims, saying the plane was instead likely brought down by a BUK missile shot by Kiev.

Russian Foreign Minister Sergei Lavrov on Monday said there were "many, many strange things" about the investigation, including the failure to get the International Civil Aviation Organisation (ICAO) to head it.

"Fragments of the plane and bodies of victims were not collected for a long time, then only some were taken and some were left," Lavrov added.

"There were no responses to the many questions that Russia sent to this investigative group," he said.

'Real reasons'

With Dutch prosecutors conducting a parallel criminal investigation, Tuesday's report will not assign blame. Instead, it will focus on four areas.

It will examine "the cause of the crash", the issue of "flying over conflict areas" and will try to answer why Dutch relatives of the victims "had to wait two to four days before receiving confirmation" that their loved ones were on board.

The report may also answer the haunting question of whether those on board knew they were about to die during the final moments of the flight, as some experts have suggested.

Families of the dead will also be confronted with the harrowing sight of a partial reconstruction of the doomed plane, made from pieces of wreckage brought back from the crash site.

BUK-maker Almaz-Antey meanwhile said it was planning to unveil the "real reasons" for the MH17 disaster at a simultaneous press conference in Moscow.

In June, the state-controlled manufacturer said that based on photos of the wreckage, a BUK was likely to have been used. But it argued it was a BUK-M1 which has not been produced in Russia since 1999.

A Ukrainian analyst told AFP he doubted Tuesday's report would have the same impact as it might have had a year ago.

"One has to understand that the geopolitical situation today is somewhat different from what it was on July 17, 2014," said Vadym Karasev, director at Kiev's Institute of Global Strategies.

With a shaky ceasefire holding in Ukraine, and with all eyes on Russia's entry into the conflict in Syria, attention is now focused elsewhere.

"Does the international community need another huge confrontation (with Russia)? Therefore, they would like to play things down with MH17," he said.