Defense Minister Kim Tae-young said there was no sign of a direct attack from rival North Korea, but military authorities have not ruled out North Korean involvement in the sinking of the Cheonan late Friday night.An explosion ripped the 1,200-ton ship apart during a routine patrol mission near Baengnyeong Island west of the peninsula. Fifty-eight crew members, including the captain, were plucked to safety; 46 remain missing.The Joint Chiefs of Staff said the exact cause would remain unclear until the ship is salvaged after the rescue operation is over. On Monday, mothers beat their chests with grief as divers went down to search for survivors, returning to report hearing no sounds inside the underwater wreckage.Kim, grilled by lawmakers on what happened Friday night, said the ship may have struck a mine left over from the war or deliberately dispatched from the North.