SYDNEY, July 31 -- Australian Prime Minister Tony Abbott said on Thursday he was confident about recovering the remains of MH17 victims despite constant blockages of the Australian-Dutch police mission to access the crash site.

The investigators were forced to abandon their mission for a fourth consecutive day because of continued fighting between Ukrainian forces and Russian-backed separatist fighters.

"I'm not sure of it, but I am confident of it," the prime minister told local radio.

Abbott said investigators are a long way from giving up all hope of ever reaching the crash site.

"We will not readily be deterred here. We are determined," he said, but added that Australia would not take unnecessary risks in recovering the bodies.