PETALING JAYA: A Sri Lankan man who forced a Malaysia Airlines flight's return to Melbourne shortly after take-off has admitted to trying to enter the cockpit by threatening to bomb the plane.

According to Australian daily The Age, Manodh Marks, 25, pleaded guilty in the Melbourne Magistrates Court on Friday (Dec 8) for attempting to take control of the Melbourne to Kuala Lumpur bound flight on May 31.

Marks caused a commotion on Flight MH128, which was carrying 337 passengers, when he attacked a female member of the cabin crew and made threats to bomb the plane.

Passengers and cabin crew on board tackled, tied-up and sat on Marks until the plane landed back at Melbourne's Tullamarine Airport.

The Age said Marks struck a plea deal with prosecutors agreeing to a single charge of attempting to take control of an aircraft.

He was said to have replied through an interpreter: "I plead guilty, your honour" when asked to enter a plea.

He faces a maximum 20 years in jail.

The report said in a plea deal, prosecutors withdrew a more serious charge of attempting to hijack an aircraft, which carries a maximum sentence of life imprisonment.

A charge of reckless conduct endangering an aircraft's safety was also withdrawn together with a third charge of threatening to destroy, damage or endanger an aircraft's safety, or to kill or injure anyone on board.

Marks is said to be currently in custody and will face the Melbourne County Court in April for a plea hearing. He has made no bid for bail.

Marks was previously said to have been mentally unstable and had been recently released from a psychiatric facility when he boarded the flight on May 31.