The top US military officer accused China Wednesday of ducking its responsibility to curb its close ally North Korea in the wake of the North's "inhumane" and deadly attack on a South Korean island.

Admiral Mike Mullen also announced plans for more joint military exercises with South Korea and said the South has the right to respond as it sees fit to any future attacks.

Asked at a press conference in Seoul if he had asked the South to exclude the option of air strikes on the North, he replied: "I did not".

Mullen, chairman of the Joint Chiefs of Staff (JCS), was visiting to show solidarity following the November 23 bombardment which killed two civilians and two marines and sparked a regional crisis.

It was the first shelling of civilian areas in the South since the 1950-53 Korean war and wrecked almost 30 homes.

Mullen, in strongly worded comments, said he would leave Wednesday evening for talks in Tokyo on defence cooperation. "I only wish China were as helpful," he said.

"The Chinese have enormous influence over the North, influence that no other nation on earth enjoys. And yet, despite a shared interest in reducing tensions, they appear unwilling to use it," the top US officer said.

"Even tacit approval of Pyongyang's brazenness leaves all their neighbours asking what will be next."

Mullen said he appreciated Beijing's offer to host an emergency meeting on the crisis of delegates to six-party nuclear disarmament talks, including the North's representative.

But he said there was no basic for resuming talks as long as the North "persists in its illegal, ill-advised and dangerous behaviour", which should not be rewarded with bargaining or new incentives.

"China has unique influence, therefore they bear unique responsibility," Mullen said.

"Now is the time for Beijing to step up to that responsibility and help guide the North and indeed the entire region toward a better future."

The United States is pressing China to use its economic and political influence to rein in the North.

Deputy US Secretary of State James Steinberg and a high-level delegation will visit Beijing next week to consult on developments on the Korean peninsula.

The US is expected to "speak to China to tell North Korea in more clear language not to make provocations", South Korean Foreign Minister Kim Sung-Hwan told reporters, upon his return from talks in Washington with Secretary of State Hillary Clinton and his Japanese counterpart.

Seoul's military was criticised for a perceived weak response to last month's attack and the defence minister stepped down. His successor Kim Kwan-Jin has vowed next time to use the South's air power to hit the North's artillery batteries.

Mullen and South Korean counterpart General Han Min-Koo, in a joint statement after talks, said the "deliberate and illegal armed attack" on Yeonpyeong island violated the UN Charter and armistice which ended the war.

The North's "inhumane actions of killing innocent civilians deserves condemnation", they added.

The military chiefs agreed to strengthen joint efforts to deter further provocation and said they would refine existing plans so they can "resolutely respond to further North Korean aggression".

A week after the two sides ended their biggest-ever naval exercise, Mullen and Han said they would continue joint war games.

The South's military is this week holding live-fire drills off its coast, ignoring the North's warnings that they could spark a war.

The distant sound of artillery firing meanwhile from the North briefly pushed down the South's stock market and the won currency Wednesday.

But Seoul's military said it appeared to be a regular artillery drill and no shells landed south of the contested Yellow Sea border.

The United States stations 28,500 troops in the South and assumes command of both countries' militaries in case of war. The South currently has an agreement to consult US forces before using its own jet fighters in combat.

"If North Korea provokes us further, we will respond with our right of self-defence, and North Korea will have to pay a dear price for such provocation," General Han said.