Prime Minister Tony Abbott fears the remains of some Australian victims of the MH17 crash haven't been collected.
A number of body and body parts are due to be transported by air from the Ukrainian city of Kharkiv to the Netherlands on Wednesday night (AEST).
But Mr Abbott said based on an inspection of the train carriages travelling from the crash zone, many of the bodies of the almost 300 victims - including Australians - were uncollected.
"It is quite possible that many bodies are still out there in the open in the European summer subject to interference and subject to the ravages of heat and animals," he told reporters in Canberra.
The prime minister has "serious concerns" about the collection of the remains.
"It has been up until now quite unprofessional," he said.
"As long as it's possible that there are any Australian remains out there we owe it to the families to do our utmost to recover them."
Air Chief Marshal Angus Houston, the prime minister's special envoy, has told Mr Abbott an international investigation of the full crash site is vital because it may uncover more human remains, personal effects or pieces of wreckage.
The full site is about 50 square kilometres and covers farm fields and villages.
"We need a large team conducting a forensic search, a proper scouring of the site to identify anything that may have been missed up until now," Mr Abbott said.
"It might be the partial remains of a loved one. It might be a small, but critical, piece of the aircraft or the missile that is the key to the investigation."
New bits of wreckage had been found as recently as Tuesday.
Such an intensive search could only be done if the site was secure, Mr Houston told Mr Abbott.
Mr Abbott said a proper forensic search could only happen if the area was properly secured.
The government is considering options to create a safe environment for the forensic search, which could involve a cordon to bar anyone except investigators from the crash site.
More work with Australia's "partners in grief" at the United Nations could be done to strengthen the UN Security Council resolution.
"(That would) make it reality that we do, in fact, bring them all home," Mr Abbott said.
Mr Abbott has asked senior officials from various agencies and "arms" to prepare options for securing the site.
He also has had discussions with other leaders from the nations impacted by the disaster.
Asked whether "many thousands" of armed troops would be needed, Mr Abbott said such a scenario was "utterly speculative".
"I would discourage any speculation along those lines," he said.
"What we're talking about here is what's necessary to ensure that we have a full forensic search."
