Satellites picked up faint electronic pulses from Malaysia Airlines Flight 370 after it went missing on Saturday, but the signals gave no information about where the stray jet was heading and little else about its fate, two sources close to the investigation said on Thursday.

But the "pings" indicated that the aircraft's maintenance troubleshooting systems were switched on and ready to communicate with satellites, showing the aircraft, with 239 people on board, was at least capable of communicating after the jet lost touch with Malaysian air traffic controllers.

The system transmits such pings about once an hour, according to the sources, who said five or six were heard. However, the pings alone are not proof that the plane was in the air or on the ground, the sources said.

An international search is under way over a vast area in the Gulf of Thailand, the Andaman Sea and on both sides of the Malay Peninsula. The United States, which has sent ships and planes, said the area may be expanding into the Indian Ocean.

"It's my understanding that based on some new information that's not necessarily conclusive - but new information - an additional search area may be opened in the Indian Ocean," White House spokesman Jay Carney told reporters in Washington.

US defense officials later told Reuters that the US Navy guided-missile destroyer, USS Kidd, was en route to Strait of Malacca, west of the Malaysian peninsula, to continue the search for the missing jet, answering a request from the Malaysian government. The Kidd had been searching the areas south of the Gulf of Thailand, along with the destroyer USS Pinckney.

A US defense official said a Navy P-3 Orion aircraft had already searched the Strait of Malacca.