Malaysia Airlines did not appear to have anticipated the sudden departure of its chief executive officer Peter Bellew.

MAS described the announcement, which was made by Irish airline Ryanair, as "unexpected."

"Malaysia Airlines takes note of the unexpected announcement by Ryanair Holdings PLC to the London Stock Exchange regarding CEO Peter Bellew," it said in a statement today.

Ryanair had announced that Bellew would return to its fold as chief operating officer effective Dec 1.

MAS, in its statement, even made reference to Bellew's commitment to stay on with the Malaysian airline expressed less than a month ago.

"At a press conference with Malaysian and international media on Sept 27, Bellew had expressed his commitment to Malaysia Airlines when asked to comment on speculation that he would rejoin Ryanair.

"He said that he was happy to be in Malaysia and that the turnaround of Malaysia Airlines would be 'the greatest achievement of my life'," said MAS.

MAS said its board of directors will convene a meeting and an announcement will be made in due course.

"Our operations and services continue as normal, and our commitment and priority remain with our customers.

"The turnaround of Malaysia Airlines remains on track and on schedule, as per the MAS Recovery Plan," it said.

Bellew, in a statement released by Ryanair, had said he was excited to return to the airline.

"I look forward to working with all the team and all the crews I know so well to further develop our growth to 600 aircraft over the next six years," he had said.

At the time of writing, Bellew had not released any other statement, including through MAS.