A CanJet Boeing 737 is seen on the tarmac of Sangster International Airport in Montego Bay earlier this week after Jamaican commandos successfully ended an attempting hijacking of the aircraft. (Adrian Wyld/Canadian Press)

A Jamaican airport is defending the actions of unarmed security guards who let a gunman board a CanJet plane over the weekend, in the airport operator's preliminary investigation into the foiled hijacking.

Questions have been raised over how the gunman managed to force his way through security at Sangster International Airport in Montego Bay on Sunday and board a Boeing 737 with 159 Canadian passengers and six crew members on board.

In a statement on Wednesday, MBJ Airports Limited said that its preliminary investigation found the airport's security team "reacted properly and followed their procedures."

It said the guards "maintained visual surveillance" of the gunman until the Jamaica Constabulary Force, which provides the armed security for the airport, arrived at the scene.

All the passengers and two crew members were freed less than an hour into the hijacking. The hostage situation ended about seven hours later on Monday morning when Canadian-trained Jamaican military commandos secretly entered the aircraft and overpowered the gunman.

The airport said the response by JCF was "exceptional, exceeding many international standards."

Government considering security upgrades

The airport is now conducting a "more detailed and exhaustive" investigation of the incident and will work with the the government and the Jamaica Civil Aviation Authority in their separate probes, it said.

Jamaican Prime Minister Bruce Golding has apologized to the passengers for their ordeal and promised a complete and thorough investigation into what he called an obvious security breakdown.

Jamaican Transport Minister Henry has said he is in discussions with Jamaica's National Security Ministry about possibly adding armed police to various points in the airport.

Stephen Fray, 21, who has been described as a "troubled young man" and mentally ill, is in police custody, though he has not yet been charged.