U.S. President Barrack Obama has directed the U.S. military to coordinate with South Korea to “ensure readiness” and deter future aggression from North Korea, White House Spokesman Robert Gibbs said on Monday.

The U.S. gave strong backing to plans by South Korean President Lee Myung-bak to punish North Korea for sinking one of its naval ships, Gibbs said in a statement.
Obama and South Korean President Lee have agreed to meet at the G20 summit in Canada next month.
-----Tension a factor in Japan base decision
Japan's prime minister suggested Monday that heightened tensions on the Korean peninsula contributed to his decision to break a campaign promise and keep a key U.S. Marine base in Okinawa. Analysts say China's growing military assertiveness may also have played a role.
U.S. Secretary of State Hillary Rodham Clinton, traveling in Beijing, commended Prime Minister Yukio Hatoyama for making ""the difficult but nevertheless correct decision"" Sunday to keep Marine Corps Air Station Futenma on the strategically important island, which is close to Taiwan and the Chinese mainland and not far from the Korean peninsula.
""I thank him for his courage and determination to fulfill his commitments. This is truly the foundation for our future work as allies in the Asia-Pacific region,"" she said from Beijing.
U.S. officials traveling with Clinton, who visited Tokyo on Friday, said the March sinking of the South Korean warship Cheonan — blamed on a North Korean torpedo — had deepened the understanding among Japanese officials about the importance of the U.S. military presence in Okinawa. The island hosts more than half the 47,000 American troops in Japan under a mutual security pact.
Recent examples of China's military flexing its muscle may have also been a factor in pushing Hatoyama to reverse his stance and reach an uncomfortable decision — which could contribute to his resignation in coming weeks or months amid plunging approval ratings.
In April, Chinese ships were spotted in international waters off Okinawa. A Chinese helicopter also came within 100 feet (30 meters) of a Japanese military monitoring vessel in the vicinity of a Chinese naval exercise.
The prime minister came to office last September promising to move the Marine base off the island, going against a 2006 agreement with Washington to transfer it to Henoko, in a less crowded, northern part of Okinawa.
Meanwhile, Japan said Monday that it backed South Korea’s decision to take Pyongyang to the UN Security Council for sinking the South Korean naval ship.
“I’m not sure about taking the lead, but I think we would strongly support (South Korea),” Chief Cabinet Secretary Hirofumi Hirano told a news conference after South Korean Korean President Lee said Seoul would take the North to the UN decision-making body.
Photo: U.S. President Barack Obama addresses the graduating class of 2010 at the U.S. Military Academy at Est Point at Mitchie Stadium in West Point, New York, May 22, 2010. (Photo: Reuters/Larry Downing)