KUALA LUMPUR, Malaysia - Malaysia's transport minister on Thursday vowed to take stern action against an air traffic control supervisor if it is confirmed that he was asleep on the job when Malaysia Airlines Flight 370 disappeared a year ago.

An interim investigation report Sunday contained transcripts of conversations between air traffic controllers and the airline that revealed confusion after the Boeing 777 dropped off radar with 239 people aboard while flying from Kuala Lumpur to Beijing.

Off radar

The last voice contact was a "good night" message from the cockpit to controllers at 1:19 a.m. on March 8. The shutdown of the transponder one minute later removed the plane's identification from commercial radar.

In one conversation four hours later, a Kuala Lumpur air traffic controller told a Malaysia Airlines official that he would need to wake up his supervisor when pressed on the exact time of the last contact with the plane. The controller came on duty after 3 a.m.

Transport Minister Liow Tiong Lai said his department viewed the matter seriously and was conducting an internal investigation, including whether the supervisor was on or off duty at the time in question.

"The work is on rotation. . . . If he is on a working shift, this is serious. We will definitely take action if there is any misconduct," he told reporters.

Awaiting report

Liow said the ministry didn't investigate the matter earlier as it was waiting for Sunday's report by the independent safety investigation team. The ministry's probe will be "very fast," he added, without saying when it would be completed.

After the last contact, the plane deviated from its flight path, turning sharply west, and then south, according to analyses of transmissions to a satellite. Despite an exhaustive search in the southern Indian Ocean where the plane was believed to have run out of fuel and crashed, no trace of wreckage has been found.

In late January, Malaysia's government formally declared the plane's disappearance an accident and said all those on board were presumed dead.