Obama met Saturday with South Korean President Lee Myung-Bak on the sidelines of global summits here, and it was at Lee's side that the U.S. president talked tough about Pyongyang.
"There has to be consequences for such irresponsible behavior," Obama said.
He said "we stand foursquare behind" Lee.
An independent report has found that the March sinking of the South Korean warship Cheonan was caused by a North Korean torpedo. Lee says he wants a "strongly worded" resolution out of the U.N. Security Council.
