Aviation authorities are expected to officially complete this year an agonizing search for a disappeared Malaysian Airlines flight that carried 239 passengers, putting closure to a two-year operation considered one of the most challenging in history.

Malaysian Prime Minister Najib Razak, in statement, marking the second anniversary of the tragedy Tuesday, said the endeavor to  look for Flight MH370 was unprecedented, and took search teams to undersea mountain ranges where they battled swift currents. 

"The current search operation is expected to be completed later this year, and we remain hopeful that MH370 will be found in the 120,000-square-kilometer [46,332-square-mile] area under investigation. If it is not, then Malaysia, Australia and China will hold a tripartite meeting to determine the way forward," Najib said, the Singapore Straits Times reported. 

RTS9N0P A woman walks past a mural of missing Malaysia Airlines Flight MH370 two years after it disappeared, in Kuala Lumpur, Malaysia, March 7, 2016. Photo: Olivia Harris/Reuters

The Boeing 777 went off radar March 8, 2014, while traveling from Kuala Lumpur, Malaysia, to Beijing, shocking the world and igniting wild theories, including of hijacking.  Of the people aboard the plane, 50 were Malaysians while the rest were Chinese and Australian passengers.

A confirmed piece of the plane’s wing was found on the French Indian Ocean island of Réunion, near Madagascar, last July.  An object that could also be debris recently washed up on the shores of Mozambique and will be taken to Australia to be examined.

That discovery offered proof that the flight "tragically ended" even as the evidence offered little comfort to relatives of  those aboard, Najib said.

"We remain committed to doing everything within our means to solving what is an agonizing mystery for the loved ones of those who were lost. On this most difficult of days, our thoughts and prayers are with the families of those who will never be forgotten," he said. "But we know that neither the passage of time, nor this evidence, will comfort those whose grief cannot be assuaged."

The Australian Transport Safety Board (ATSB) previously said the plane's wreckage could  “very likely” to be found by July.  The claim was based on its judgment that MH370 would have crashed in the southern Indian Ocean, off the Western Australia coast.

 "I do not think it possible to fully understand how difficult the past two years have been for the friends and families of those on board the aircraft," Australian Transport Minister Darren Chester added Tuesday, Agence France-Presse reported. "The sense of loss is something they live with on a daily basis. A tragedy such as MH370 touches people from all over the world and today we are united in remembering all 239 people who were on the flight."

Theories about the airliner also abound, with one Russian newspaper, Moskovsky Komsomelets, reporting  that the plane had been taken over by unknown terrorists and flown to Afghanistan, where the crew and passengers were being held captive. Others speculated that the plane was hijacked and deliberately crashed, with two of the passengers traveling with stolen passports.

Relatives and families of the passengers, who banded together as Voice 370, had urged Malaysia to press on with the search, saying stopping was unacceptable. 

"We believe that they should not throw in the towel, close this case and simply chalk it up as an unsolvable mystery," Voice 370 said on its Facebook page last week.