French investigators said they have abandoned a second round of search efforts for the black box flight recorders from Air France Flight 447, believed to be resting in the depths of the Atlantic.

The Airbus jet crashed into the ocean June 1 en route from Rio de Janeiro to Paris, killing all 228 people aboard. The flight's voice and data recorders could provide important clues as to what precipitated the accident, whose cause has so far stumped investigators.

The French accident investigation agency, known as the BEA, said in a statement that the research ship leading the hunt for the plane's flight recorders had left the site, more than 1,450 kilometers off Brazil's northeastern coast. The ship, the Pourquoi Pas, was to arrive Thursday in Dakar, Senegal.

The statement said the second phase of search efforts, focusing on the underwater hunt for debris and the black boxes, "has finished." Investigators and experts will gather in the coming weeks to determine whether to launch a third phase.

"We have not found the wreckage, we have not found the recorders," said BEA spokeswoman Martine del Bono.

She said the BEA will gather a team of about 10 specialists from several countries including Brazil, France, the United States and Germany, to study the data gathered from the second phase and decide what a third search phase would cost and require.

She gave no estimate on when an eventual third mission might begin.

The investigation "is far from finished," she said. "We must find" the black boxes, she added.

During the first phase of the search, rescuers recovered 50 bodies and more than 600 pieces of the plane scattered on the sea.

The second phase of the search began after the black boxes stopped emitting signals, about a month after the crash.

It was led by the Pourquoi Pas, operated jointly by the French Navy and the French Research Institute for Exploration of the Sea. It has a manned submarine, the Nautile, a remote-controlled robot, the Victor 6000, and special sonar.

Airbus promised to help fund a third phase of the search over a wider area if necessary.

A preliminary report into the crash said the plane hit the ocean intact and belly first at a high rate of speed. But without the flight recorders, investigators may never fully understand what happened. Investigators have said there were no signs of explosion or terrorism.