Malaysia and Australia say they remain “hopeful” that flight MH370 will eventually be found, two years on from its disappearance.
The aircraft disappeared between Kuala Lumpur and Beijing on 8 March 2014 with 239 people on board.
Australian-led search teams are combing a 120,000 sq km (46,330 sq mile) area of the southern Indian Ocean.
Only one confirmed piece of debris, a part of wing called a flaperon, has been found, on Reunion Island.
The search, involving Australian, Chinese and Malaysian experts, is estimated to have cost more than $130m (£92m).
It is expected to draw to a close later this year if there is no progress, although many relatives of passengers want it to continue.
Malaysian Prime Minister Najib Razak said on Tuesday he was hopeful of solution to the mystery, but that the search had been the hardest in aviation history.
“We remain committed to doing everything within our means to solving what is an agonising mystery for the loved ones of those who were lost,” he said in a statement.
Australian Transport Minister Darren Chester also expressed hope, saying finding the plane would “give answers to the world, in particular the families of missing loved ones, about what happened”.
Relatives of 12 Chinese passengers of the missing Malaysia Airlines flight MH370 have filed lawsuits in Beijing, saying they want the courts to help establish what happened.
Zhang Qihuai, the lawyer for the 12 families, said they were seeking a range of damages, but their goal was to determine the cause of the accident and those who were responsible.
Families of 32 other passengers, mostly Chinese, filed a separate lawsuit in Malaysia, their lawyer has said.
Under international agreements, relatives have two years following an air accident to begin legal action.
Martin Dolan, the head of the Australian Transport Safety Bureau which is co-ordinating the search, has said it will receive a piece of suspected plane debris found in Mozambique, early next week.
It will be analysed by Australian experts, with representatives of the plane’s manufacturer Boeing and the Malaysian investigation team advising.
An interim report into the search will be released by Malaysian investigators later on Tuesday.