Wooden coffins were being brought out on the tarmac of a Ukrainian airport as the first plane carrying corpses recovered from the crash site of Malaysian flight MH17 readied to leave for the Netherlands.

Grieving families and Dutch royals were due to receive the bodies on Wednesday as flags flew at half mast on a day of mourning across the nation, which lost 193 citizens in the flight that was allegedly shot down, turning civilians from a dozen nations into casualties of a remote conflict raging in eastern Ukraine.

Speaking from Eindhoven, where the bodies will arrive, Al Jazeera's David Chater said all of the bells of the Netherland's churches will ring, and a trumpet will be played as the plane lands.

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"The royal family will attend along with about 1,000 relatives of the victims. There will be a huge mix of emotions as people don't know who the victims are.

"A convoy of hearses will take the bodies to another military base at Hilversum, where DNA samples will be collected. The identification process could take several weeks or even months."

US officials said the Malaysia-bound plane from Amsterdam was mistakenly shot down by pro-Russian separatists as investigators hoped two black boxes, which have been sent to Britain for analysis, would help to shed light on the disaster that killed all 298 on board.

The recovery of the crucial flight recorders and the victims' remains came after pro-Russian separatists finally released them under international pressure.

But officials said many remains were still on the sprawling crash site in rebel-held territory, decomposing under the summer heat.

Evidence gathered by US intelligence officials suggests pro-Russian separatists launched the SA-11 surface-to-air missile that blew up the Malaysia Airlines flight on Thursday, but it remains unclear "who pulled the trigger" and why.

"The most plausible explanation ... was that it was a mistake," and that the missile was fired by "an ill-trained crew" using a system that requires some skill and training, said a senior intelligence official who spoke on condition of anonymity, AFP news agency reported.

Bodies left at site

A truce has been declared by rival sides around the crash impact site, but international investigators still face massive obstacles.

Dutch officials confirmed receipt of only 200 of the 298 victims' bodies.

International monitors said more remains were left in the vast crash site, littered with poignant fragments from hundreds of destroyed lives.

"There were human remains that had not been picked up," said Michael Bociurkiw, a spokesman for European security body OSCE's mission to Ukraine after visiting the scene.

Australia's prime minister Tony Abbott said the remains of some victims of the Malaysian airliner crash may never be recovered unless there was a thorough search of the site.

Russia, which US officials accuse of backing the separatists by providing them with military hardware and training, has faced a hail of international condemnation over the accident.

The crash has spurred a propaganda war, with both Ukraine and Russia trading blame, ratcheting up tensions after months of crisis sparked when Kiev turned its back on its former Soviet master in favour of stronger European ties.

Russia denies supporting the rebels who have declared independence in parts of Russian-speaking eastern Ukraine and also says it did not supply the missile system allegedly used to bring down MH17.

US intelligence officials said Russian claims that the Ukrainian government had shot down the plane were "not plausible" noting that the territory was clearly under rebel control.

A senior security official in Kiev claimed that Russia had massed over 40,000 soldiers along its border over the past week.

Source: Al Jazeera and agencies