WASHINGTON (Reuters) - President Barack Obama has directed the U.S. military to coordinate with South Korea to “ensure readiness” and deter future aggression from North Korea, the White House said on Monday.

President Barack Obama addresses the graduating class of 2010 at the U.S. Military Academy at West Point during the 2010 commencement ceremony at Mitchie Stadium at West Point, New York, May 22, 2010. REUTERS/Larry Downing

The United States gave strong backing to plans by South Korean President Lee Myung-bak to punish North Korea for sinking one of its naval ships, White House spokesman Robert Gibbs said in a statement.

The White House urged North Korea to apologize and change its behavior, he 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,” Gibbs said.

“U.S. 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,” he said.

Obama and Lee have agreed to meet at the G20 summit in Canada next month, he said.

Late last week, a team of international investigators accused North Korea of torpedoing the Cheonan corvette in March, killing 46 sailors in one of the deadliest clashes between the two since the 1950-53 Korean War.

Lee said on Monday South Korea would bring the issue before the U.N., whose past sanctions have damaged the already ruined North Korean economy.

The United States still has about 28,000 troops in South Korea to provide military support.

The two Koreas, still technically at war, have more than 1 million troops near their border.

“We will build on an already strong foundation of excellent cooperation between our militaries and explore further enhancements to our joint posture on the Peninsula as part of our ongoing dialogue,” Gibbs said.

Gibbs said the United States supported Lee’s plans to bring the issue to the United Nations Security Council and would work with allies to “reduce the threat that North Korea poses to regional stability.”

Obama had also directed U.S. agencies to evaluate existing policies toward North Korea.

“This review is aimed at ensuring that we have adequate measures in place and to identify areas where adjustments would be appropriate,” he said.