PETALING JAYA • Former Malaysian prime minister Najib Razak said investigators had "never ruled out" the possibility that the pilot of Flight MH370 might be responsible for the disappearance of the Malaysia Airlines aircraft, but had not publicly said so as there was no conclusive proof, a Malaysian news site quoted him as saying yesterday.

Najib spoke to Free Malaysia Today (FMT) in response to comments by former Australian prime minister Tony Abbott, who claimed in an interview that Malaysia's top leadership considered from the outset that the disappearance of MH370 in 2014 was a case of mass murder-suicide by the pilot.

Senior government MP Lim Kit Siang said yesterday that the "highest levels" of the past government should speak up over the issue.

Najib told FMT that the authorities had in their probe looked into the background of MH370 pilot Zaharie Ahmad Shah and into his political affiliations with then opposition parties, but the suspicions were not made public.

"It would have been deemed unfair and legally irresponsible since the black boxes and cockpit voice recorders had not been found and hence, there was no conclusive proof whether the pilot was solely or jointly responsible," said Najib, who was the prime minister when the plane vanished six years ago with 239 people on board.

"Again I must stress that this possible scenario was never ruled out during the search effort and investigations, where no effort was spared," he told FMT.

"The pilot is a known active opposition party member who had attended various political activities and the opposition leader had admitted later that the pilot was related to him," Najib said, referring to MP Anwar Ibrahim, who was then facing his second sodomy trial.

The plane had gone missing a day after Datuk Seri Anwar was sentenced to jail following the Court of Appeal's decision to overturn his acquittal on a charge of sodomising his former aide Mohd Saiful Bukhari Azlan.

In a documentary on Sky News, Mr Abbott said: "My very clear understanding from the very top levels of the Malaysian government is that from very, very early on here, they thought it was murder-suicide by the pilot."

Mr Abbott declined to name any individuals to support his claim.

Flight MH370 vanished on March 8, 2014, on its way to Beijing from Kuala Lumpur.

Satellite data showed that the jet abandoned its normal route shortly into the flight.

The Malaysian government's 2018 report into the disaster said that the aircraft systems were probably manipulated and investigators could not rule out "intervention by a third party", reported Bloomberg.

Meanwhile, Datuk Seri Azharuddin Abdul Rahman, who was the former director-general of the Department of Civil Aviation - now called the Civil Aviation Authority of Malaysia - when the plane went missing, said that Mr Abbott was reopening wounds of families and friends of those who went missing as the tragedy remained a mystery.

"The theory of mass murder-suicide was one of the theories but it has yet to be proven," said Mr Azharuddin, when asked to comment on the matter.

"I met Abbott during the course of MH370 investigations but I have never confirmed such theories nor spoken to him personally."

The former Malaysian official added: "He claimed the top leadership in Malaysia then told him so - ask him who those people are.

"I am surprised he is raising this theory now - for what purpose, I do not know."