Bringing MH17 perpetrators to justice difficult, Aussie envoy says

Australia's lead envoy in the investigation into the MH17 tragedy has spoken of the difficulty of finding the perpetrators.

Air Chief Marshal Angus Houston said newly retrieved pieces of wreckage from the terrorist attack, which killed 38 Australians and 298 people overall, would show what happened when the plane was brought down on July 17.

But he warned that the "very challenging criminal investigation" is a much tougher prospect.

"What I will say is that I know that every lead in the investigation will be pursued and I think that will give us the best chance of finding the perpetrators," he said.

"But there are certain realities and limitations about this that make it exceedingly difficult because of the mere fact that the crash site is in the middle of a war zone."

Air Chief Marshal Houston was speaking as Ukrainian President Petro Poroshenko met Australian officials involved in the investigation into the disaster.

The president thanked Australia for its support in the war in Ukraine but called for further help in getting Russian troops out of his country.