RECIFE (Brazil) - FRANCE has said it was sending a nuclear-powered submarine and a vessel carrying two deep-sea research subs to hunt for the plane's black boxes, believed to be sitting on the sea bed up to 6,000 meters underwater.

Meanwhile, more ships and planes joined the search on Friday for debris from an Air France flight that came down in the Atlantic, Brazilian officials said.

A total of 12 planes are now sweeping the zone 1,000 kilometers off Brazil's northeast coast, as well as three Brazilian navy vessels and a helicopter, Brazil's air force said in a statement.

Two other navy ships were on their way.

The planes include a French aircraft, 'Atlantic Rescue D,' which was joining the Brazilian air force effort, it said.

So far, no debris from the flight has been recovered by the ships, though Brazilian officials have said that pieces from Air France flight 447 were spotted earlier this week in the area. No bodies have been spotted.

Air force officials said weather in the zone had deteriorated, with rain limiting pilots' visibility to 4,000 meters.

The sea was choppy, with waves as high as 1.8 meters.

The Airbus A330 went down early Monday, as it was flying between Rio de Janeiro and Paris with 228 people on board. -- AFP