Parts of the plane have been found
The USNS Mary Sears, which has been helping hunt for the missing Boeing 737, detected a distinctive signal from the boxes on the ocean floor.
The Adam Air flight, which went missing halfway through its flight from Java to Sulawesi, had 102 people on board.
Parts of the plane have been washed up off the west coast of Sulawesi.
The Mary Sears located signals "on the same frequency" as the flight recorders of the missing plane, the US embassy in Jakarta said in a statement.
The ship also "detected heavy debris scattered over a wide area", which is being analysed to verify whether it is the missing aircraft, the statement added.
HUNT FOR MISSING JET 1 Jan: Plane goes missing 2 Jan: Reports that wreckage has been found prove false 3 Jan: Search resumes 5 Jan: Search area is expanded 8 Jan: Metal spotted in sea 10 Jan: US ship joins search 11 Jan: Fishermen find debris 25 Jan: Flight recorders found
Indonesia's transport perils
Information from the flight recorders could help investigators determine the cause of the crash.
Officials said the government would now have to decide whether to try and retrieve the boxes from the ocean bed.
"We do not have the technology to retrieve the black boxes," Setio Rahardjo, chairman of the National Commission on Transport Safety told AFP news agency.
"Assuming we have the funds, then we have to ask for a country who has sophisticated technology, such as the US," he added.
Meanwhile, the search has entered the fourth week in the Java Sea for a ferry which sank at the end of December - about 300 passengers are still missing.
A flight data recorder.
The United States military may have found the Black Boxes from a missing Indonesian jetliner that went missing on January 1, 2007.

Using ultrasonic pinger signals, the USNS Mary Sears located debris on the bottom of the ocean that match the signal that they are using to find the boxes. 

"We have detected heavy debris scattered over a wide area," said the U.S. embassy in Indonesia in a statement. Other debris may also have been located at least 1,000 meters below the oceans surface.

"During the search of the projected crash site of Adam Air Flight 574, the Mary Sears, using a Towed Pinger Locator, detected pingers on the same frequency of the black box associated with the missing airplane," added the statement.

Despite the announcement, Indonesia's transport safety board denies receiving any reports that the boxes have been found.

"One thing is for sure, up until this second, I have not received any report from the (Indonesian) liaison officers who were onboard the ship," said Indonesian air force commander who is in charge of the ongoing search to find the plane, Eddy Suyanto.

The largest piece of the plane to be recovered so far, is the tail of the plane, which was discovered by a fisherman. Trays and seats have also been recovered, but so far none of the bodies of the passengers or crew have been found.

The plane, a Adam Air Boeing 737-400 went missing, in flight from Surabaya, on the island of Java, to Manado on the island Sulawesi. All 102 people on board the plane are believed to have been killed.

Just 1 day after the plane crashed, false reports that the wreckage was found on land and 12 survivors were found had began to circulate. The 12 people that were reported to have been survivors, turned out to be the remaining survivors of a ferry crash in the same area 4 days before the plane was reported missing.

The cause of the crash is still not known, and investigations are ongoing.