Dutch experts on Tuesday prepared to take custody of some 280 bodies recovered from downed Malaysian flight MH17, as a train carrying the remains arrived in the government-held Ukrainian city of Kharkiv.

Rebels controlling the crash site released the morgue train under intense international pressure, finally allowing a great majority of the 298 crash victims to begin the long journey home.

Their remains are now to be flown to the Netherlands, which had 193 citizens on board the doomed flight and is taking the lead in investigating a disaster that has brought Ukraine's bloody three-month conflict to the doorstep of countries as far away as Australia.

Pro-Russian separatists -- who stand accused of bringing down the aircraft, possibly with a missile supplied by Moscow -- bowed to a furious clamour for the bodies and black boxes to be handed to investigators five days after the crash.

The rebel concessions came as European foreign ministers were meeting in Brussels to weigh possible new sanctions against Russia for its perceived support of the insurgency rocking ex-Soviet Ukraine.

Both black boxes, which record cockpit activity and flight data, were handed to Malaysian officials by the prime minister of the self-proclaimed Donetsk People's Republic, Alexander Borodai, before scores of journalists.

As world leaders denounced the "shambolic" situation at the crash site, international experts finally managed Monday to inspect the bodies, kept in refrigerated train cars away from the sweltering summer heat, before they left for Kharkiv.

Local truce

Borodai also announced a ceasefire within 10 kilometres of the impact site, hours after Kiev's pro-Western authorities said they would halt all fighting in a broader zone.

The localised truce will at last allow international monitors to examine the vast area, a forensic minefield littered with poignant fragments from hundreds of destroyed lives.

Elsewhere in Ukraine's east, fighting between government forces and rebels continued unabated with local authorities in the besieged cities of Donetsk and Lugansk reporting 10 civilians killed in 24 hours.

In a sign tensions are still running high a senior security official in Kiev claimed that Russia had massed over 40,000 soldiers along its border over the past week.

Black boxes 'intact'

Despite the apparent progress in getting the investigation going, leaders warned the rebels' handling of the crash site had already done much damage.

Australian Prime Minister Tony Abbott, whose country had 28 citizens and nine residents on the plane, said: "There is still a long, long way to go."

"After the crime comes the cover-up," he added. "What we have seen is evidence tampering on an industrial scale. That has to stop."

Experts from Malaysia, reeling from their flagship carrier's second disaster in only four months after flight MH370 went missing in the Indian Ocean, said the black boxes were "intact with only minor damage."

"We have not found the black boxes from flight MH370, so (we) are happy to be able to recover these," said a member of the Malaysian team.

Malaysia's deal with the pro-Russian rebels caps a disaster response praised at home as swift and clear, unlike the widely mocked handling of missing flight MH370.

But the flag carrier Malaysian Airlines had to defend itself after confirming it diverted a flight over Syrian airspace when its usual route over Ukraine was closed following the crash.

The airline said in a statement that MH4's flight path over Syria was along a route approved by the UN's aviation agency.

Russian riposte

In Brussels, European foreign ministers were meeting to discuss possible new sanctions against Russia, which has been accused by the United States of supplying the missile allegedly used to shoot down the plane.

Obama put the onus on Moscow to lift the suspicions weighing upon it, saying President Vladimir Putin must prove "that he supports a full and fair investigation".

An under-fire Moscow hit back, saying records showed a Ukrainian military plane was flying three to five kilometres from the Boeing 777 before it crashed.

"With what aim was a military plane flying along a civilian aviation route practically at the same time and at the same flight level as a passenger liner?" asked Lieutenant-General Andrei Kartopolov.

Ukraine's President Petro Poroshenko dismissed the suggestion the army was to blame, calling it an "irresponsible and false statement" by Russia.

The US embassy has confirmed as authentic recordings by Kiev of an intercepted call between an insurgent commander and a Russian intelligence officer as they realised they had shot down a passenger jet.

The Washington Post said Ukraine's counterintelligence chief had photographs and other evidence that three Buk M-1 anti-aircraft missile systems moved from rebel-held territory into Russia less than 12 hours after the crash.

The separatist uprising is the latest chapter in a prolonged crisis sparked by Kiev's desire for closer ties with the EU, a goal many in the Russian-speaking east do not share.