The navy destroyer was badly damaged in the collision with a Philippine-flagged cargo ship off the Japanese coast early on Saturday.

The bodies of the US sailors were found in flooded sleeping berths a day after the accident which tore a huge gash in the side of the warship.

Japanese investigators have been interviewing the Filipino crew of the Japanese-operated ACX Crystal, and hope to directly hear accounts of crew members of the Aegis-equipped USS Fitzgerald.

The United States has primary jurisdiction in investigating accidents involving its military.

“Our probe is still under way, and we are discussing” with the US authorities over interviews with American sailors, a Japanese coastguard official said on Tuesday.

They were also investigating why the cargo ship took nearly an hour before reporting the collision.

Originally, the Japan Coast Guard believed the crash occurred at 2.20am on Saturday but its crew members have later told Japanese investigators that the incident happened at 1:30 am.

Japanese officials are also analysing why the 222-metre ACX Crystal made a 180 degree turn at about 2.00am and made another turn after it reported the accident at about 2.20am, as shown in data from the Marine Traffic website.

It was not immediately clear what prompted the sharp turn.

“As to the chronological order of what happened and other details we are still investigating,” the coastguard spokesman said, declining to elaborate further.

Richardson was also planning to meet with Japanese Marine Self-Defence Force and coast guard officials to express his appreciation for assisting in search efforts, Kyodo News reported.