US also gave a strong support to the decisions taken by South Korea to punish the North for sinking the naval ship, Cheonan.
The White House spokesman Robert Gibbs said, "We endorse President Lee's demand that North Korea immediately apologize and punish those responsible for the attack, and, most importantly, stop its belligerent and threatening behavior. US support for
South Korea's defense is unequivocal and the president has directed his military commanders to coordinate closely with their Republic of Korea counterparts to ensure readiness and to deter future aggression."
White House also urged North Korea to apologize and change its behaviour towards South Korea. Obama and Lee have agreed to meet at the G20 Summit in Canada in June.
Gibbs also said that US will build on the already strong foundation of excellent cooperations with South Korean military and explore further enhancements to their joint posture on the Peninsula as a part of their ongoing dialogue.