Two more pieces of debris were all but confirmed Thursday to be from flight MH370, adding fresh clues to the mystery of the Malaysia Airlines plane which is presumed to have crashed at sea.

The fragments washed up on beaches in South Africa and Mauritius in March and brought to the Australian Transport Safety Bureau's laboratories for testing.

After an expert examination they were found to have "almost certainly" come from the fated Boeing 777 aircraft, which vanished en route from Kuala Lumpur to Beijing on March 8, 2014 with 239 passengers and crew on board.

Five pieces of debris have now been identified as either definitely or probably from the jet, all discovered thousands of kilometres from the ongoing search zone, likely swept there by currents.

The latest breakthrough follows a wing part recovered last year from the Indian Ocean island of Reunion, which neighbours Mauritius, and confirmed by Malaysian authorities as from MH370.

Since then two more items found about 220 kilometres (140 miles) apart from each other in Mozambique in December 2015 and February 2016 have been examined.

The ATSB has said these too were "almost certainly" from the Malaysian plane.

One of the new parts, washed up at Mossel Bay in South Africa, was an aircraft engine cowling, identified from a partial Rolls-Royce stencil.

While there was no direct link on the cowling unique to MH370, the ATSB said the stencil was consistent with those developed and used by Malaysian Airlines.

Mossel Bay is more than 2,000 kilometres (1,250 miles) from Vilankulo, the Mozambican resort where one of the earlier pieces of debris was found.

The other part, which came ashore on Rodrigues island in Mauritius, was a decorative laminate from a "work table" in the main cabin, used by no other Boeing 777 customer than Malaysia Airlines.

Given this, the ATSB concluded that "part no.3 was a Malaysian Airlines Boeing 777 engine cowling segment, almost certainly from the aircraft registered 9M-MRO", which operated as MH370.

"Part no.4 was a Malaysian Airlines Boeing 777 panel segment from the main cabin, associated with the Door R1 closet, almost certainly from the aircraft registered 9M-MRO."

- Still hopeful -

One of the pieces found in Mozambique, which had a number stencilled on it, was identified as a segment from a Boeing 777 flap track from the right wing, with the stencilling conforming to that used by Malaysia Airlines.

The other, which had the words "No Step" on it, was part of a Boeing 777 horizontal stabiliser panel with stencilling also consistent with that used by the carrier.

Australia is leading the painstaking search for the plane in the remote southern Indian Ocean, believed to be its final resting place, and has so far scoured 105,000 square kilometres of deep ocean floor without finding any trace.

Australian Transport Minister Darren Chester remained optimistic that more evidence could be found, offering hope to devastated next-of-kin still grasping for answers.

"The Australian government will continue to work closely with the Malaysian government and the People's Republic of China in our efforts to locate the missing aircraft," he said.

"We remain hopeful the aircraft will be found."

Despite this, if nothing turns up once the designated 120,000 square kilometre zone is fully searched, it is likely to be abandoned, Australia, Malaysia and China have jointly said.

In an operational update this week, Australia said three ships continued to hunt for the plane but winter weather had set in, with waves up to 12 metres (39 feet) and high winds hampering them.

mp/grk/ds

Malaysia Airlines

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