The U.S. Navy has picked up signals from the flight data recorders of an Indonesian jetliner that crashed into the sea on New Year's Day with 102 people onboard, the U.S. Embassy said Thursday.

The USNS Mary Sears located signals "on the same frequency of the black boxes associated with the missing airplane," a statement issued by the U.S. Embassy in Jakarta said.

Data from the flight recorders will be crucial in determining the cause of the crash, but retrieving them from the ocean floor at a depth of more than a mile will likely be a difficult, expensive and lengthy operation.

The Adam Air Boeing 737 went missing more than three weeks ago after reporting heavy winds off the western coast of Sulawesi while on flying from Indonesia's main island of Java.

Three Americans — a man from Oregon and his two daughters — were aboard the plane.

Search teams have since found almost 200 pieces of debris — mostly small pieces of the wings, tail, cockpit and cabin — but no bodies.

The embassy did not say when the signals were picked up or where on the ocean floor off Sulawesi they were coming from.

The hull of the aircraft has not yet been recovered, but the statement said the Mary Sears "detected heavy debris scattered over a wide area" close to where the signals were coming from.

Eddy Suyanto, the Indonesian air force commander in charge of the search and rescue mission, said he had not been formally told of the ship's findings.

"One thing is for sure, up until this second, I have not received any report from the (Indonesian) liaison officers who were on board the ship," he said.

Indonesia said earlier this week it did not have a submarine capable of retrieving the recorders and would have to rent one.

The devices on commercial jetliners record crucial flight data such as a plane's speed and altitude as well the voices of the pilots.

The embassy said that "having completed its mission," the Mary Sears would now depart Indonesian waters on Jan. 26.