Whereabouts Of N. Korean Subs Still Unknown

Two North Korean submarines that evaded U.S. and South Korean surveillance earlier this week have returned to their base after a drill in the Sea of Japan, reports the Yonhap News Agency (South Korea).

Two other 300-ton submarines, however, remain unaccounted for, said an unnamed South Korean defense source.

South Korea has raised its alert level since the sinking of the Cheonan corvette in late March by a suspected North Korean torpedo launched from a submarine.