Malaysian Police Chief Khalid Abu Bakar said Sunday that background checks of passengers on Malaysian Airlines Flight 370 had come up empty for suspects, but he added that not every country with nationals onboard had responded to requests for information. Authorities also said they had begun searching a much larger area than the first week of the hunt had focused on.

"The search area has been significantly expanded," acting Transport Minister Hishammuddin Hussein said. "From focusing mainly on shallow seas, we are now looking at large tracts of land, crossing 11 countries, as well as deep and remote oceans."

On Sunday, authorities appealed for help in searching from the Caspian Sea to the far south of the Indian Ocean. No trace of the Boeing 777-200ER has emerged since the plane vanished on March 8 with 239 people onboard, but investigators believe that someone who knew how to switch off the communications and tracking systems may have diverted the flight.

Electronic signals that the plane continued to exchange periodically with satellites suggest that it could have continued flying for nearly seven hours after leaving the range of Malaysian military radar off the country's northwest coast, heading towards India. The plane had enough fuel to fly for about eight hours, Malaysian Airlines Chief Executive Ahmad Jauhari Yahya said.

'All your resources'

On Sunday, Malaysian officials briefed ambassadors from 22 countries. Although several nations have become involved in the high-tech search, the request marks a new diplomatic phase in a search operation thought increasingly likely to rely on the sharing of sensitive material such as military radar data.

"The meeting was for us to know exactly what is happening and what sort of help they need," TS Tirumurti, India's high commissioner to Malaysia, told the news agency Reuters. "It is more for them to tell us: 'Please put in all your resources.'"

Police have begun investigating the personal, political and religious backgrounds of the pilots, crew and ground staff. On Saturday, police special branch officers searched the homes of the captain, 53-year-old Zaharie Ahmad Shah, and first officer, 27-year-old Fariq Abdul Hamid, in middle-class suburbs of Kuala Lumpur close to the international airport.

Colleagues have described the experienced pilot Zaharie as an aviation enthusiast who spent his off days operating a life-sized flight simulator he had set up at home. Khalid, the police chief, said investigators had taken the flight simulator for examination by experts.

On Sunday, Malaysian Defense Minister Hishammuddin Hussein said at the news conference that that someone told air traffic controllers "All right, good night" just after the shutdown of one of the plane's automated reporting systems. Whoever spoke did not mention any trouble. Major General Affendi Buang of Malaysia's air force told reporters he did not know whether the pilot, the co-pilot or someone else had spoken those words.

mkg/rc (Reuters, AFP, dpa, AP)