In a new twist to sudden disappearance of a Malaysia Airlines plane, authorities today said intelligence agencies are probing how four persons with fake identities boarded the aircraft and counter-terrorism agencies of other countries have been alerted about it.

The red flags were raised yesterday when it was found that four passengers with suspect identities were able to board the plane that went missing over the South China Sea en route to Beijing from Kuala Lumpur.

Defence Minister and acting Transport Minister Hishammuddin Hussein said authorities were looking at four possible cases of suspect identities. On two impostors who boarded the flight using passports lost by an Italian and an Austrian, he said the authorities would screen the entire manifest of the flight.

Inspector-General of Police Khalid Abu Bakar said police have not classified terrorism attack behind the disappearance of the plane but are not ruling out any possibilities.

There are still no confirmed information about the fate of the plane after about 36 hours passed.

Meanwhile, a Vietnamese helicopter discovered two oil slicks in waters off the coast of Vietnam, an official with the search operation confirmed today. The oil slicks were spotted at the suspected area where a China-bound Malaysia Airlines plane went missing.