US vows to back South Korea at UN

But Clinton stopped short of detailing what measures would be sought at the Security Council, where China, a veto-wielding member and a North Korean ally, is expected to block attempts to impose new sanctions on the isolated North.

“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,’’ Clinton said at a news conference after meetings with the South Korean president, Lee Myung Bak, and Foreign Minister Yu Myung Hwan. “I believe that the Chinese understand the seriousness of this issue and are willing to listen to the concerns expressed by both South Korea and the United States.’’

She acknowledged a complicated task facing Washington and Seoul when she said the allies have to work on two tracks simultaneously. She spoke of the “immediate crisis’’ of the sinking that “requires a strong but measured response’’ and of a “longer-term challenge of changing the direction of North Korea, making a convincing case to everyone in the region to work together to achieve that outcome, denuclearizing the Korean Peninsula, and offering the opportunities for a better life for the people of the North.’’

North Korea has denied any role in the sinking of the ship and the loss of 46 South Korean sailors.

Clinton also endorsed Lee’s “right approach’’ in trying to avoiding “escalation and a broader conflict’’ while seeking international support to punish the North.

“The key word’’ during the South Korean leaders’ meetings with Clinton was her strategy of “strategic patience,’’ said Lee Dong Kwan, Lee’s spokesman.

“Another way to put it is that time is on our side,’’ the spokesman said after the president’s meeting with Clinton. “We shouldn’t go for an impromptu response to each development but take a longer-term perceptive in shaping the situation around the Korean Peninsula.’’

Those comments followed an escalation of tension in the past week, with the South cutting off most trade with the North and the North responding by terminating all communications with the South and threatening to launch artillery shells across the border.

Yesterday, the North Korean military threatened to “completely block South Korean personnel and vehicles’’ from a joint industrial park in the North Korean town of Kaesong if the South carries out its plan to resume its psychological warfare against the North, mainly through propaganda broadcasts across the border. Continuing its sharp language, it also said that it would attack and destroy the propaganda loudspeakers to be put up along the border by the South, calling them a “military provocation.’’

Eight South Korean government officials returned to Seoul after they were expelled from Kaesong yesterday.

But the South Korean government noted that, despite the North’s declaration that it was severing communications with the South, yesterday it followed its usual procedure of speaking through a military telephone line across the border to approve the entry of hundreds of workers from the South to work their regular shifts at the industrial complex. Neither country seemed to take the final step, at least yet, of dismantling the Kaesong complex, the last sign of progress they made in improving relations over the past decade, and losing the tens of thousands of jobs it creates for the North.

Clinton did not elaborate on what would be the appropriate action at the Security Council.

“This was an unacceptable provocation by North Korea and the international community has a responsibility and a duty to respond,’’ Clinton said.

She spent only a few hours in Seoul, but speaking at the news conference alongside Yu, she said, “We will stand with you in this difficult hour, and we will stand with you always.’’

China and the United States on Tuesday had wrapped up three days of high-level meetings in Beijing with a handful of trade and energy agreements but with little progress on the most pressing US priority: winning China’s backing for new measures against North Korea. In Beijing, Clinton said China would take “a period of careful consideration in order to determine the best way forward in dealing with North Korea as a result of this incident,’’ suggesting that there was little expectation for joint action to condemn the attack.