US says North Korea shelling tied to succession

A top US military officer says North Korea's artillery attack on a South Korean island is linked to the succession of the reclusive state's leadership.

Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, said the United States was working with allies on ways to respond but said: "It's very important for China to lead. The one country that has influence in Pyongyang is China and so their leadership is absolutely critical."

A U.S. nuclear aircraft carrier is en route to South Korea to carry out scheduled war games in a show of force against North Korea.

The nuclear-powered USS George Washington, which carries 75 warplanes and has a crew of over 6,000, left a naval base south of Tokyo on Wednesday morning to join planned joint exercises with South Korea.

The decision to send the aircraft carrier came less than 24 hours after the North Korean shelling of South Korea's island of Yeonpeyong killed two marines.

The attack attracted a wave of international condemnation for what the White House described as an "outrageous act" of provocation.

President Barack Obama and his South Korean counterpart Lee Myung-bak agreed to hold the joint military exercises following a telephone conversation in which the US reiterated its security guarantees to Seoul.

The controversial exercises in the Yellow Sea, already postponed once after objections from China last August, could raise the stakes further on the tense Korean peninsula.

"This exercise is defensive in nature," US Forces in Korea said in a statement. "While planned well before yesterday's unprovoked artillery attack, it demonstrates the strength of the ROK (South Korea)-US alliance and our commitment to regional stability through deterrence."