THE search area for the missing Malaysian airliner in the southern Indian Ocean has been refined based on new analysis.

But the investigation into how Malaysia Airlines Flight 370 came to crash cannot proceed until the wreckage and black boxes are recovered, officials have said.

Australia's deputy prime Minister Warren Truss said analysis of a failed attempted satellite phone call from Malaysia Airlines to Flight 370, which disappeared on March 8, "suggests to us that the aircraft might have turned south a little earlier than we had previously expected".

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The overall search area still remained unchanged, he said. He did not elaborate on how that analysis was achieved.

Mr Truss and Malaysian transport minister Liow Tiong Lai have signed a memorandum of understanding on co-operation in the search for the missing Boeing 777.