Crews have extinguished all known fires aboard a U.S. Navy warship that burned for four days at its mooring in San Diego, a top admiral said on Thursday, but it was still unclear if the Bonhomme Richard could be saved.

Firefighters were combing through the 844-foot-long (257-m) amphibious assault ship to make sure that all flames were out before a formal investigation could begin into the cause of the blaze, Rear Admiral Philip Sobeck told a news briefing at U.S. Naval Base San Diego.

“We do not know the origin of the fire. We do not know the extent of the damage. It is too early to make any predictions or promises of what the future of the ship will be,” said Sobeck, commander of the Navy’s Expeditionary Strike Group Three.

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The flames erupted on Sunday morning, followed by at least one large explosion aboard the Bonhomme Richard, which was commissioned in 1998 with a name dating to the U.S. Revolutionary war.

Sobeck said 63 people – 40 sailors and 23 civilians – were treated for minor injuries during the four days of firefighting from land, air and sea that followed, Sobeck said. None were hospitalized.

Read more: Reuters