SEOUL, South Korea - U.S. Secretary of State Hillary Rodham Clinton said Wednesday that the world has a duty to respond to the sinking of a South Korean warship, which has been blamed on North Korea.
After talks with South Korean leaders Wednesday, Clinton told reporters the attack that killed 46 sailors was an "unacceptable provocation" by the North and the "international community has a responsibility and a duty to respond."
Clinton was spending just a few hours in Seoul discussing possible international responses to the crisis.
The North denies it was responsible and has threatened to retaliate if action is taken against it. It has previously warned of "all-out war."
On Wednesday, North Korea pledged to close the last road link with the South if Seoul continues with anti-Pyongyang propaganda broadcasts.
"The South Korean puppet war-like forces would be well advised to act with discretion, bearing deep in mind that such measures of the KPA (army) will not end in an empty talk," North Korea's KCNA news agency quoted a top official as saying.
N. Korean subs off radar
Despite the harsh language, South Korea's military said Wednesday there were no signs of unusual activity by North Korean troops.
At least two cross-border communication links were operating normally on Wednesday morning, according to Seoul's Unification Ministry.
Four North Korean submarines, however, have disappeared from South Korean radar since they left their eastern coastal base Thursday, the mass-circulation Chosun Ilbo newspaper reported citing an unidentified Seoul official.
The paper said South Korea's military was trying to track down the location of the submarines, but the Joint Chiefs of Staff said it could not confirm the report.
A Seoul-based monitoring agency reported Tuesday that North Korean leader Kim Jong Il ordered the country's 1.2 million-member military to get ready for combat. South Korean officials could not immediately confirm the report.
North Korea often issues fiery rhetoric and regularly vows to wage war against South Korea and the United States.
Clinton said the ship sinking "requires a strong but measured response," but she did not elaborate.
She said the United States would consult with South Korea and members of the U.N. Security Council on what the appropriate action would be, but she declined to offer a timeline for action.
"We're very confident in the South Korean leadership and their decision about how and when to move forward is one that we respect and will support," she said.
Clinton called the investigation into the sinking, which killed 46 sailors, "very thorough, highly professional" and "very convincing."
She said both the United States and South Korea had offered China "additional information and briefings about the underlying facts of that event."
"We hope that China will take us up on our offer to really understand the details of what happened and the objectivity of the investigation that led to the conclusions," Clinton said.
She touched down in the South Korean capital Wednesday after intense discussions on the deteriorating situation with Chinese officials in Beijing.
South Korea wants to bring North Korea before the U.N. Security Council over the sinking, and has U.S. support.
Tensions have risen since last week, when a team of international investigators concluded that a torpedo from a North Korean submarine tore apart the Cheonan warship off the west coast on March 26.
The sinking of the Cheonan was one of the South's worst military disasters since the Korean War.
The South has announced a set of measures against Pyongyang in response to the sinking of the Cheonan.
Those include, after a six-year lull, using speakers near the border to broadcast anti-government propaganda and send messages across by balloon.
However, the North is allowing South Korean workers to enter a joint industrial park that is a lucrative source of income for the Pyongyang government.
The move suggests the isolated North is being careful not to take steps that will cause it real material damage.
But if it does cut the road link to the Kaesong industrial park, it will be unable to function.
Analysts say both Koreas, who have never repeated the open conflict of the 1950-53 Korean War, were unlikely to let their current hostility turn to war.
Apart from Kaesong, there is little economic relationship left between the two, their ties almost frozen since the South's conservative President Lee Myung-bak took office in 2008.
"North Korea is not closing up Kaesong immediately because it is saving the cards it needs in order to play the game," said Jang Cheol-hyeon, researcher at the Institute for National Security Strategy.
By paying the workers' wages directly to Pyongyang, Kaesong is one of the few major legitimate income sources for the North's secretive leaders, worth tens of millions of dollars a year.
China's cool response
Clinton arrived in Seoul after wrapping up two days of intense strategic and economic talks with China, which responded coolly to U.S. appeals that it support international action against North Korea over the warship sinking.
The North and South have technically remained at war since the 1950-53 Korean War ended with an armistice rather than a peace treaty.
The U.S. and South Korea are planning two major military exercises off the Korean peninsula in a display of force intended to deter future aggression by North Korea, the White House said. The U.S. has 28,500 troops in South Korea.
Relations are at their lowest point since a decade ago, when South Korea began reaching out to the North with unconditional aid as part of reconciliation efforts. Lee has taken a harder line since taking office in 2008, and the South has suspended aid.