The Malaysian government formally declared the disappearance of Malaysia Airlines Flight 370 to be an accident Thursday, saying that it believed all 239 people on board had died. 

Malaysia civil aviation chief Azharuddin Abdul Rahman said Thursday that the search for the jet "remains a priority." The announcement was made in a pre-recorded message broadcast on Malaysian television with what Azharuddin called "the heaviest heart and deepest sorrow."

The announcement fulfills a legal obligation that will allow efforts at compensation claims to proceed. 

The plane was traveling to Beijing from Kuala Lumpur when it disappeared on March 8 of last year without a trace. No sign of the plane has been found despite a massive underwater search operation in the southern Indian Ocean off the western coast of Australia. The hunt resumed in October after a four-month hiatus with more sophisticated sonar equipment.

Azharuddin said the searchers, led by Malaysia, China and Australia, pursued every credible lead and reviewed all available data that tracked the plane to a remote corner of the southern Indian Ocean, but were still unable to locate it.

He said that Chapter 1 of Annex 13 to the Convention on International Civil Aviation, commonly referred to as the "Chicago Convention," states that the definition of the term "accident" includes "the aircraft is missing".

"It also states that `an aircraft is considered to be missing when the official search has been terminated and the wreckage has not been located."'

Azharuddin said the investigation by the safety team and Malaysian police were ongoing, but both were limited by the lack of physical evidence at this time, particularly the flight recorders.

"At this juncture, there is no evidence to substantiate any speculations as to the cause of the accident," he said, adding that an interim report detailing the progress of the safety investigation will be released soon.

The Associated Press contributed to this report.