'Industrial scale' tampering of evidence at MH17 site: Australia

Abbott, whose government was behind a UN Security Council resolution that Monday unanimously demanded full access to the site in rebel-held east Ukraine, admitted progress had been made but said more needed to be done.

"There is still a long, long way to go," he told a press conference of the quest to repatriate bodies and bring those responsible for the 298 deaths to justice.

"After the crime comes the cover-up," he added.

"What we have seen is evidence tampering on an industrial scale. That has to stop."

His comments came as pro-Russian separatists, who are accused of shooting down the plane, finally conceded to a furious international clamour for the bodies and the jet's black boxes to be handed over to international investigators.

It followed days of bitter wrangling in which rebels hampered experts from gaining access to the site and were accused of tampering with evidence.

"This site has been trampled from the beginning and we haven't just seen all sorts of random individuals roaming around the site, picking over the remains, picking over the wreckage. We've seen heavy equipment coming onto the site," Abbott said.

"The more recent footage suggests it's more like a building demolition. And this again is unacceptable."

In recent days Abbott had been particularly scathing in his criticism of Russian President Vladimir Putin for failing to intervene, but admitted he now appeared to be acting following intense international pressure.

"The point I made 24 hours ago is that President Putin had said all the right things. I then went on to say the challenge is to hold him to his word," he said.

"And to President Putin's credit, he has thus far been as good as his word. I give him credit for being as good as his word over the last 24 hours."

A train carrying the remains of 280 people killed in the disaster was finally allowed to leave a rebel-held region in eastern Ukraine Tuesday as the militants declared a truce around the crash site.