China has been working to keep tensions between North and South Korea from escalating following a Northern artillery attack on the South on Tuesday.

China's foreign minister Yang Jiechi has met North Korea's ambassador and spoken on the phone to his US and South Korean counterparts.

Officials say China's priority is to avoid a recurrence of Tuesday's attack on Yeonpyeong Island, which killed four people.

Tomorrow the nuclear-powered aircraft carrier USS George Washington, with its 75 planes and crew of 6,000, will take part in massive naval war games.

North Korea has warned this will push the region to the brink of war and is threatening to launch fresh attacks if it is sufficiently provoked.

But it is playing a dangerous game. This week it killed four South Koreans in an artillery attack and in March it torpedoed a South Korean naval ship killing 46 sailors.

In what could be a crucial development, state-owned newspapers in China have blamed North Korea for this week's attack; one even editorialised that North Korea could be a country without a future.

If the North continues to resort to military strikes out of the blue, it will eventually lead to a more brutal response from Seoul. Adding nuclear weapons into the mix, the deadly standoff is well short of being resolved.

China has also voiced its displeasure at the participation of a United States aircraft carrier battle group in tomorrow's war games.

But South Korea and its American allies are keen to put on a show of strength.

The North yesterday started firing fresh volleys of artillery two days ahead of the war games, sending South Korean residents who remain on Yeonpyeong Island running to air raid shelters.

The sound of fresh rounds of artillery emanating from North Korea led to fears of a fresh attack.

But the South Korean government has said that this seemed to be a training exercise and that no shells landed on its territory.

Tensions high

The US commander in South Korea, General Walter Sharp, has called on North Korea to stop its attacks.

"What I've seen here is basically North Korea attacked this island, which is a clear violation of the armistice agreement," he said.

"We and the United Nations command will investigate this completely and will call on North Korea to stop any future attacks."

The hope is that Pyongyang's warning is just aggressive rhetoric from the North, but the South is bolstering its troop numbers in border regions just in case.

The South Korean government of Lee Myungbak has been criticised, even by some in its own party, for not responding to this week's artillery attack with enough force.

This is despite the fact that it fired 80 shells back across the border at the time. There has been no information about what damage this caused in the North.

South Korea's former defence minister Kim Yae-yong defended the decision not to call an airstrike on the North's artillery positions that fired on Yeonpyong, saying he did not want to risk starting a full-scale war.

He has now resigned, accepting full responsibility for what has been described as an inadequate response.