Opposition leader Datuk Seri Anwar Ibrahim condemned on Tuesday speculation that the captain of the missing Malaysia Airlines (MAS) flight MH370 may have been driven by political motives to sabotage the plane.

Describing Captain Zaharie Ahmad Shah as a "decent man", Anwar said he was "disgusted" by what he saw as an attempt to smear the pilot and somehow implicate the opposition party in the March 8 disappearance.

The investigative spotlight has focused on Zaharie and his co-pilot, Fariq Abdul Hamid, since it became clear that the plane was deliberately diverted from its intended flight path to Beijing by someone on board.

Multiple media reports have noted Zaharie, 53, was an active member of Anwar's Parti Keadilan Rakyat (PKR), and some have suggested he might have sabotaged the flight as an act of political revenge.

In a highly controversial case, Anwar was convicted of sodomy just hours before MH370 took off.

"Is it a crime for anyone to be a member of Keadilan?

"I of course did not take the news reports seriously but I am speaking out because I sympathise with the pilot and his family," he said.

On Monday acting Transport Minister Datuk Seri Hishammuddin Tun Hussein denied an allegation that Malaysia has held back information about the missing Flight MH370's movements.

Speaking at a press conference he said the priority has always been to find the aircraft and authorities would not withhold any information that could help.

He added authorities however have a responsibility to not release information until it has been verified by the international investigations team.