U.S. officials have not yet validated data from the black boxes of an Ethiopian Airlines plane that crashed killing all 157 people on board, emphasizing the investigation remains in the very early stages, two officials briefed on the matter told Reuters Sunday.

Earlier on Sunday, a spokesman for the Ethiopian Transport Ministry said the data from the black boxes was successfully recovered and teams from the United States and Ethiopia had validated it.

Citing analysis of the black boxes recovered from the wreckage of the March 10 disaster, the spokesman said the crash had "clear similarities" with October's Lion Air crash.

Investigators are trying to determine why the aircraft plunged into a field shortly after takeoff from Addis Ababa, searching for possible similarities to an October Lion Air crash that killed 189 people.

The National Transportation Safety Board and Federal Aviation Administration are assisting the investigators. The officials said after investigators reviewing black box data return to Addis Ababa and start conducting interpretive work, the NTSB and FAA will assist in verification and validation of the data, the officials said.

NTSB spokesman Eric Weiss did not immediately comment Sunday on the report that the NTSB had "validated" some data but said "As the U.S. accredited representative to the Ethiopian-led investigation, the NTSB is a full partner during this fact-finding phase."

"That includes providing assistance in analyzing the FDR data, working to develop a transcript from the CVR, processing and documenting on-scene evidence and participating in interviews."

The FAA said Wednesday that some physical evidence recovered at the scene was part of the government's decision to order the planes' grounding.