FILE PHOTO: Men unload a case from a diplomatic car from the Ethiopian Embassy outside the headquarters of France's BEA air accident investigation agency in Le Bourget, north of Paris, France, March 14, 2019. The black boxes from the crashed Ethiopian Airlines Boeing 737 MAX 8 arrived in France on Thursday. REUTERS/Philippe Wojazer/File Photo

WASHINGTON (Reuters) - U.S. safety investigators have reviewed data from the flight recorders or black boxes that were aboard crashed Ethiopian Airlines Flight 302, four people briefed on the investigation told Reuters.

The National Transportation Safety Board has reviewed raw data from the flight data recorder and listened to the cockpit voice recorder, the sources said. The review was reported earlier by ABC News. A preliminary report is expected as early as next week, U.S. officials said.

Under international rules, Ethiopia safety officials are in charge of the investigation and are the only entity that can release information about the probe. An NTSB spokesman declined to comment on Thursday.

Boeing unveiled new software upgrades and training on Wednesday after two fatal crashes of Boeing 737 MAX 8 airplanes in five months led regulators around the world to ground the planes, including the U.S. Federal Aviation Administration.

The March 10 Ethiopian Airlines crash that killed all 157 on board has set off one of the widest inquiries in aviation history and cast a shadow over the Boeing MAX model intended to be a standard for decades. It followed an October crash of a 737 MAX operated by Indonesia’s Lion Air, which plunged into the Java Sea after takeoff from Jakarta, killing 189.

NTSB chairman Robert Sumwalt told a U.S. Senate panel on Wednesday that the board was getting all the cooperation it needed from the Ethiopian and Indonesian governments.

“I have no indication at all that the Ethiopians are not sharing with us the information that we need,” Sumwalt said.

It is unclear how long it may take the FAA and other international regulators to decide when to allow the 737 MAX to resume flying, but officials first want details from the preliminary findings of the Ethiopian crash. The FAA also has not yet formally received Boeing’s proposed software upgrade.