North Korea fired artillery into its west coast waters on Wednesday briefly pushing down nervous South Korean financial markets but they quickly recovered after media reports said it was only a military drill.
A South Korean military official said: "At 9:04 am an unknown number of artillery shells fell on the North's side of the NLL (North Limit Line)".
The firing, which local media said was a military drill, came just over two weeks after the North bombarded a South Korean island near their disputed border off the west coast of the divided peninsula.
News of the firings hit local shares and the won. Both later recovered.
It came as the top US military official visited Seoul where he pressed China to act like a world leader and tame its ally North Korea, warning that the "bad guy" from Pyongyang will continue to try to destabilise the region.
Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, went to the South Korean capital to show his "commitment and solidarity" to the US ally after North Korea's attack and revelations of its nuclear advances.
In an indication of the flurry of diplomatic activity since the North's bombardment of a South Korean island, the Washington Post reported that New Mexico Governor Bill Richardson, a former special envoy to North Korea, may visit Pyongyang next week for a "private chat with top officials at the invitation of key people in the nuclear crowd over there".
Mullen's trip to South Korea and Japan follows talks in Washington on Monday between Secretary of State Hillary Clinton and her Japanese and South Korean counterparts. All three voiced grave concerns over the North Korean attacks and called on China to take action against its wayward ally.
On Tuesday, Beijing hit back at the United States and its Asian allies for their refusal to talk to North Korea, saying dialogue was the only way to calm escalating tension on the divided Korean peninsula.
But Mullen said the Chinese must do more because "their economy is dependent on stability".
"They are a world leader and leaders must lead -- particularly to prevent crises and to prevent the kinds of destabilising activities that are very evident coming out of the leadership in Pyongyang," he said.
China views the North as a strategic buffer against the US-allied democracy South Korea and is Pyongyang's largest trade partner and benefactor.
Deputy Secretary of State Jim Steinberg will lead a US delegation to China next week to try to persuade Beijing to put more pressure on Pyongyang despite Chinese fears that this may destablilise North Korea, a US official said.
Washington, Seoul and Tokyo have been lukewarm towards Beijing's proposal for emergency talks between the six regional powers, worried that they could be seen as rewarding Pyongyang for its deadly attack on a South Korean island two weeks ago.
More Provocations Likely
Mullen added there is "no doubt in my mind (provocations) will continue unless leaders step forward and put Pyongyang in a position where they realise their behavior has to change".
"This guy's a bad guy and when you're dealing with bad guys, you can't wish away what they're going to do," Mullen said of the North's iron ruler Kim Jong-il.
"Because of the actions taken by North Korea recently ... they're making (the region) a more dangerous place," he added.
As South Korea staged its own live-fire drills around the country, Mullen was to meet senior Seoul military officials and President Lee Myung-bak. Lee said he wants to turn the island that was attacked last month, as well as four others nearby, into "military fortresses".
Mullen said he wanted to review the various US-South Korea military drills planned in coming months and work with Seoul to calm the situation.
"A very significant part of our discussions and goals is to keep any actions limited to those that would not escalate…because no one wants this to break out of control and conflict to break out," said Mullen.