French Prime Minister Francois Fillon said on Tuesday it is still unclear what caused the disappearance of the Air France Airbus.

"No theory is favored at the moment," Fillon told the French parliament.

"Our only certainty is that the plane did not send out any distress call, but regular automatic alerts sent for three minutes indicated the failure of all systems," he said.

France is also sending more aircraft to the disaster area for search and rescue, he added.

The French parliament observed a moment of silence Tuesday to honor the victims aboard the Airbus A330. A church service will be held in Notre-Dame cathedral in Paris on Wednesday.

The Air France Airbus A330-200, Flight 447, bound for Charles de Gaulle airport in Paris, lost contact with the control center shortly after its takeoff from Rio de Janeiro on Sunday at 7:00 PM local time (2200 GMT).

Earlier, Air France said in a statement that the plane, carrying 216 passengers and 12 crew members, "crossed through a thunderous zone with strong turbulence" at around 0200 GMT Monday, and "an automatic message was received at 0214 GMT signaling electrical circuit malfunction.

(Xinhua News Agency June 3, 2009)