Sporadic fighting in Ukraine is adding to the difficulty of identifying and repatriating Australians who died in the MH17 crash.

Fighting in Ukraine has delayed the transfer of bodies to investigators seeking answers to the MH17 crash and the repatriation of almost 300 dead.

A refrigerated train carrying the remains of Australian and other victims of the Malaysia Airlines flight left a rebel-controlled town in eastern Ukraine bound for the country’s second-biggest city, Kharkiv, where it will be met by Australian officials.

However, Dutch forensic experts in Kharkiv told AAP the operation would take longer than expected because of fighting.

The BBC reported that pro-Russian militants were firing mortars and rockets in Donetsk and at least one civilian had died in the past six hours.

Australian Prime Minister Tony Abbott says when the train arrives in Kharkiv it will allow Operation Bring Them Home to start in earnest.

The bodies will be flown almost immediately to the Netherlands where an international team, including forensic experts from Australia, will identify the dead.

Malaysian investigators also have two black boxes from the flight, which will shed light on cockpit conversations and flight data in MH17’s final moments.

Up to 39 Australian citizens and residents were among the 298 people killed when MH17 was downed, likely by a missile fired by Russia-backed separatists.

The delay comes despite assurances from Russia of full co-operation and its support for an Australia-authored UN Security Council resolution.

Mr Abbott said he was concerned that “industrial scale” evidence-tampering at the crash site would hamper the investigation.

While the UN resolution was a good step forward, there was still a “long, long way to go” before the crash site was properly secured and justice was done.

“After the crime comes the cover-up,” Mr Abbott said.

The prime minister noted that Russian President Vladimir Putin had declared in the past 24 hours that everything possible must be done to provide security for international experts at the crash site.

Australian police have been gathering DNA from the families of victims to help with the identification of bodies when officers arrive in the Netherlands.

Mr Abbott promised the government would be “erring on the side of generosity” when it came to compensating the families, some of whom he has telephoned personally.

The prime minister was among many dignitaries to sign a condolence book at Parliament House on Tuesday.

“Twenty-three million Australians share the sadness of those who mourn,” he wrote.

The UN resolution also condemned the attack and extended the international community’s deepest sympathies and condolences to the families of the victims.

Foreign Minister Julie Bishop, who has received credit for the success of the UN resolution, said the families were owed answers.

Australian and Dutch aircraft will be involved in flying the bodies to the Netherlands, which lost almost 200 people on MH17.