PARIS - Investigators have not yet found flight recorders of an Air France airliner that crashed this month, France's air accident authority said on Tuesday after a report that signals from the recorders had been picked up.

The website of France's Le Monde daily reported that signals had been detected and a mini submarine had been launched to try to locate the black box recorders that could contain vital clues to explain the June 1 crash, in which 228 people died.

But the BEA, the French air accident authority, said searchers had not heard any signals they could be sure came from the black boxes.

No signals transmitted by the flight recorders' locator beacons have been validated up to now, it said in a statement.

In the context of the sea searches that are under way, work is undertaken on a regular basis that is aimed at eliminating any doubts related to any sounds that may be heard, and any findings will be made public, it said.

Everyone aboard died when the Air France Airbus 330 crashed into the Atlantic en route from Rio de Janeiro to Paris on June 1.

A BEA spokeswoman noted that many sounds are detected on the seabed and said investigators had picked up numerous signals that had turned out to be false leads.

Locator beacons, known as pingers, on the flight recorders send an electronic impulse every second for at least 30 days. The signal can be heard up to 2 km (1.2 miles) away.

French vessels involved in the search operation include a nuclear submarine with advanced sonar equipment and a research ship equipped with mini submarines.

The remote location in the Atlantic as well as the depth and surface of the ocean floor have made the search especially difficult and the wreckage could lie anywhere between 1 km (0.6 miles) and 4 km (2.5 miles) down.

(Reporting by James Mackenzie, Editing by Janet Lawrence)