Malaysia said it had conferred with the US and Chinese ministers on the search for Malaysian Airlines Flight MH370, an unprecedented 26-nation operation that now spans Asia from the Caspian Sea to the southern Indian Ocean.
Investigators are convinced that someone with deep knowledge of the Boeing 777-200ER and commercial navigation diverted the jet, carrying 12 crew and 227 mainly Chinese passengers, perhaps thousands of miles off course.
China's ambassador to Malaysia said the country had carried out a detailed probe into its nationals aboard the flight, which vanished on March 8, and could rule out their involvement.
"The probe into the incident's cause is not suitable to be conducted in a high-profile way," Ambassador Huang Huikang told Chinese reporters, state television said on one of its official microblogs on Tuesday.
US and European security sources said efforts by various governments to investigate the backgrounds of everyone on the flight had not, as of Monday, turned up links to militant groups or anything else that could explain the jet's disappearance.
A European diplomat in Kuala Lumpur also said trawls through the passenger manifest had come up blank.