Fighting may make MH17 mission impossible

Prime Minister Tony Abbott says the MH17 recovery mission could become impossible if fighting between Ukrainian forces and pro-Russia separatists escalates.

A joint team of Australian, Dutch and Malaysian officials again successfully accessed the MH17 crash site on Tuesday. A total of 27 Australian Federal Police officers were part of the latest search.

But while both sides of the conflict continue to observe a ceasefire at and around the crash site, nearby fighting intensified as Ukrainian troops reached the main rebel stronghold of Donetsk.

"If the place erupts in all-out war obviously it would be very difficult if not impossible to complete our mission," Mr Abbott told ABC radio on Wednesday.

He says he cannot yet say how many Australian bodies have been retrieved from the site.

"The explosion, the deceleration, the descent, the impact does terrible things to bodies. So we are talking - and I regret to speak this way - we are talking about body parts here," he said.

"What we need to do is gather all of the human remains and then go through the very painstaking process of matching DNA to work out whose remains we have recovered."