Investigators looking into the causes of the downing of Malaysia Airlines flight MH17 last week said they have found no evidence the airliner's black box voice recorder had been tampered with.

"The Cockpit Voice Recorder was damaged but the part that contains the data was intact," the Dutch Safety Board said in a statement. "Nor was there any evidence or indication that (it) had been manipulated."

The board said it would now work on assessing the information it had downloaded from the black box, a process which would need more time. It said examination of the airliner's other black box, the Flight Data Recorder, would start tomorrow.

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