SEOUL: South Korea’s president today ordered the military on alert for any moves by rival North Korea after the defence minister said last week’s explosion and sinking of a South Korean ship may have been caused by a North Korean mine.

The blast ripped the 1,200-ton ship apart last Friday night during a routine patrol mission near Baengnyeong Island, along the tense maritime border west of the Korean peninsula. Fifty-eight crew members, including the captain, were plucked to safety; 46 are missing, with dim prospects for finding any further survivors. Divers geared up to break into the ship today, Rear Adm Lee Ki-sik of the Joint Chiefs of Staff said. He said there were no signs of life inside.

Officials say the exact cause of the explosion remains unclear, and US and South Korean officials said there was no outward indication of North Korean involvement.

However, Defence Minister Kim Tae-young told lawmakers yesterday that a floating mine dispatched from North Korea was one of several scenarios for the disaster.

“Since the sinking took place at the front line, the military should thoroughly prepare for any move by North Korea,” President Lee Myung-bak told his Cabinet, according to his spokesman. “I want the military to maintain its readiness.” The Joint Chiefs of Staff said the cause of the blast may remain unclear until the ship is salvaged after the rescue operation is over.