The search for the missing Malaysia Airline flight MH370 could take years, a senior US defence official has warned.
The statement was made as search teams failed to find any trace of the missing jet or black boxes.
A US navy submersible drone has been searching the southern Indian Ocean's seabed within a six-mile radius of the spot where a signal thought to come from a black box was detected, around a month after flight MH370 went missing on 8 March, The Guardian reports.
Nearly 95 percent of the target seabed area has been scoured by the Bluefin-21 drone, which has been unsuccessful in finding any sign of the wreckage of the plane.
The unnamed US official said that the team searched the focused area and found nothing, adding that now it would again have to go back to searching the big area that will take years.
Meanwhile, officials at the search centre in Perth said in a statement that if no contacts of interest are made, Bluefin 21 will continue to examine the areas adjacent to the six-mile radius.
The officials said that they are currently consulting very closely with their international partners on the best way to continue the search into the future.