Tokyo - The US Navy on Tuesday paid tribute to seven sailors who were killed when their destroyer collided with a merchant ship off Japan.The Japan-based 7th Fleet said more than 2 000 sailors and their families attended the ceremony in Yokosuka, south of Tokyo. They lined the streets waving flags in memory of the victims.Further questioningThe USS Fitzgerald, carrying nearly 300 crew and Philippine-flagged container ship ACX Crystal collided in waters off Yokosuka in the pre-dawn hours of June 17. Severe damage to the right side and bottom of the guided-missile destroyer flooded the berths of 116 sailors. Navy divers found the bodies of the seven in the ship after it returned to Yokosuka.The container ship has left Yokohama, where it was investigated by Japanese authorities, for repairs of its damaged bow at an unspecified shipyard in Japan, its owner, Dainichi-Invest Corp said. It said the ship's captain and several other crew stayed behind for further questioning by the Japanese coast guard.Admiral Scott Swift, commander of the US Pacific Fleet, surveyed the ship's damage and praised its crew for saving it from sinking, it said."It's stunning that while we mourn the loss of the seven sailors, that more were not lost," Swift said in a statement. "There was no understanding of what had happened at the moment of impact ... but there was complete understanding of what needed to be done".The collision occurred in an accident-prone area known for congestion with ships trying to reach Tokyo by daybreak.Container shipThe cause of the crash is still under investigation. Japanese coast guard officials say they are eyeing possible professional negligence, but so far their interviews of the container ship's captain and crew - all Filipinos - have been on a voluntary basis.The US Navy is investigating what happened aboard the warship, while Japanese authorities are investigating the container ship and its crew.