Malaysian investigators are checking the identity of four passengers on a missing Malaysia Airlines flight, but have not yet determined if the plane was downed by an attack, the country's transport minister said on Sunday.
"All the four names are with me," Hishamuddin Hussein, who is also defence minister, told reporters.
(Read more: Anxious searching after Malaysian flight vanishes)
He added that investigators were looking at the possibility of an aircraft turnback.
He confirmed that Malaysian investigators had met counterparts from the U.S. FBI, and said the investigation was focusing on the entire passenger manifest.
"We are looking at all possibilities," he said. "We cannot jump the gun. Our focus now is to find the plane," he said.
Early Saturday, Malaysian Airlines flight MH370 vanished from the radar en route from Kuala Lumpur to Beijing.
A six-country search off the Vietnamese coast for the missing Boeing 777-200ER, the 227 passengers and 12 crew on-board yielded nothing so far aside from sighting of an oil slick, which Hussein has confirmed.