Vietnamese planes have spotted two large oil slicks in the sea near where a Malaysian jet vanished.
EPAVietnamese planes have spotted two large oil slicks in the sea near where a Malaysian jet vanished.
Malaysia has launched a terror probe into the disappearance of a passenger jet carrying 239 people and the United States has sent the FBI to investigate, as anguished relatives beg for news of their loved ones.
Six Australians and two New Zealanders are among the missing passengers.
Malaysia Airlines flight MH370 vanished from radar early on Saturday somewhere at sea between Malaysia's east coast and southern Vietnam. Search teams were still hunting for the plane, and the airline said it was "fearing the worst".
Concern over a possible security breach grew as Malaysia's government said it was investigating four people who were on the Boeing 777 plane.
At least two passengers boarded using stolen European passports, officials and reports have said.
"At the same time our own intelligence have been activated, and of course, the counter-terrorism units ... from all the relevant countries have been informed," Malaysia's acting transport minister Hishammuddin Hussein told reporters.
The Federal Bureau of Investigation is sending agents and technical experts to assist the probe, US media reported.
US officials told The Los Angeles Times that they were trying to determine whether there was any terror link to the flight's disappearance, but stressed there was no evidence to support that yet.