Here's the latest update:

"Of the four possible causes — internal explosion, collision with a reef, explosion of a naval mine or a torpedo attack — the government considered a mine most likely, a Cheong Wa Dae official said yesterday [Monday].

"Judging from what the captain of Cheonan said and the condition of the ship, the possibility of a naval mine explosion seems a bit higher than the other three," the official said. "But we are looking into all possibilities for now."

Even if the explosion were caused by a naval mine, it would be difficult to determine underwater whether it was placed by South or North Korea, he said.

"It could have been a mine that we placed and failed to retrieve, or it could have been a North Korean mine that drifted from the North," the official said. "It would be hard to confirm underwater who laid it."

Several survivors from the sunken ship reportedly ruled out the possibility of an internal explosion or a collision with a reef, drawing attention to the scenarios of a mine explosion or a torpedo attack."

Charley Noble