State investment agency Khazanah Nasional says Malaysia Airlines' chief operating officer has been promoted to become its new CEO.

Khazanah, the airline's key shareholder, said in a statement Thursday that Peter Bellew's appointment will ensure "continuity and further progress" in the airline's restructuring.

Bellew, a former RyanAir executive, will replace Christoph Mueller, who stepped down due to "changing personal circumstances." Mueller will be on leave and formally step down in September, far ahead of the end of his three-year contract.

"Proud day. Just been appointed CEO of Malaysia Airlines. We will fix it," Bellew tweeted.

The national airline has suffered years of financial losses and was hit by two air disasters in 2014 before it was taken private by Khazanah.