This would suggest that US investigators suspect foul play.

Until now the US National Transportation Safety Board (NTSB) has looked into the case, but officials say the investigation of the cockpit voice recorder has raised their suspicions that the plane was brought down as a result of a criminal act.

Investigators have synchronised the cockpit voice recorder with the flight data recorder and determined that someone in the cockpit - apparently the co-pilot - said a prayer about going into death just before the autopilot disengaged.

An official close to the investigation told the news agency AP that this was a possible sign that the plane was deliberately brought down by a crew member.

NTSB chairman Jim Hall said his team was concentrating its efforts on determining whether it should stay on the case.

However, a BBC correspondent in Washington says investigators are still officially refusing even to confirm the words recorded by the plane's black box.

They want to listen more carefully to the tape, which has been difficult to decipher.

'Pull with me, pull with me'

The BBC's Tom Carver reports: "The cock-pit voice recorder holds the key to this tragedy"

The tape reportedly indicates that the pilot had left the cockpit, returning shortly afterwards and asking "What is going on?"

Taking back the controls, the pilot is said to have issued the order: "Pull with me, pull with me." Experts say this is a command that would normally be given to bring an aircraft out of a steep dive.

Click here to see a graphic showing the last seconds of the EgyptAir flight

"We are concentrating our efforts on determining from the evidence, including the cockpit voice recorder, whether or not this investigation is to remain under the leadership of the National Transportation Safety Board," Mr Hall told a news conference.

The NTSB is responsible for investigating accidents but law enforcement agencies take over if a crime is suspected.

BBC Washington correspondent Richard Lister: "Hall refused to elaborate on his statement"

"I assure you that the National Transportation Safety Board, as well as the many other agencies of the United States government, and the government of Egypt are committed to an early resolution of this matter," Mr Hall said.

The authorities have been able to examine Flight 990's voice recorder, but no conclusions have been officially drawn from it.

Suicide, fighting in the cockpit, or an attempted hijacking are unlikely to have caused the airliner's plunge into the Atlantic off the coast of Massachusetts, reports say.

The voice recorder might still hold clues

The pilots reportedly "talked like pals" as they attempted to repair a problem in the cockpit after an alarm sounded, the NTSB chairman said on Sunday.

The tape, recovered from the seabed on Saturday, was in "good condition" and contained about 31.5 minutes of data, but "no conclusions" could be drawn from the initial reviews, Mr Hall said.

Puzzling questions

The BBC's Richard Lister: "The investigators will enhance and analyse every sound on the tape"

The flight's recorder tape is at the National Transportation Safety Board headquarters in Washington after being retrieved by the US Navy from the plane's wreckage, about 100km off the Massachusetts island of Nantucket.

A key task will be to correlate the timings between the flight recorder, retrieved last Tuesday, and the cockpit voice recorder.

Co-pilot Adel Anwar chatted with the pilot

Mr Hall said: "We're certainly hopeful that within the next two or three days we'll be able to answer a lot of the puzzling questions that information on the flight data recorder has raised in our minds."

Crash investigators hope the recorded cockpit conversations will reveal whether the plane's automatic pilot and engines were deliberately turned off.

Information gleaned from the flight data recorder indicates both engines cut off eight seconds after the autopilot disconnected.

But Boeing says the engines could only be turned off intentionally.

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