South Korean civic group members shout slogans today during an anti-North Korea and pro-U.S. rally in front of Foreign Ministry in Seoul.

SEOUL, South Korea — Secretary of State Condoleezza Rice said today she will not presume to tell South Korea or China exactly how they should enforce U.N. sanctions on North Korea, but called on all nations to cooperate.

"I did not come to South Korea nor do I go anyplace else to try to dictate to governments what they ought to do," she said at a news conference.

She said the United States wants to lower tensions, not escalate them.

Rice's South Korean counterpart, Foreign Minister Ban Ki-moon, warned North Korea anew that it should do nothing to worsen tensions.

"A second nuclear test by North Korea should never take place," he said following meetings with Rice.

Rice is on an Asian tour in support of United Nations sanctions on North Korea for a nuclear test that rattled the world amid continued signs that North Korea may be preparing for a second nuclear test.

At the same time, she is reassuring Seoul that the United States stands behind its pledge to defend the country if the North attacked. She carried a similar message in Japan, her first stop on a four-day trip devoted almost entirely to crisis talks on the nuclear threat.

Acknowledging that different countries will take different approaches to enforcing the U.N. restrictions on North Korea, Rice said the United States wants to ensure that all nations cooperate.

She said initial reports that the U.N. sanctions would require a blockade or embargo on North Korean goods were exaggerated and that there is a model for action, citing an existing agreement among about 80 nations that is meant to counter the spread of nuclear materials or long-range missiles.

South Korea has not signed on to that 2003 agreement, the Proliferation Security Initiative, out of concern that it would provoke the North. Frustration over that position was one cause of tension between Washington and Seoul even before the nuclear test.

Rice described that existing program as "effective, but not confrontational."

"There are many ways to implement (U.N. sanctions) that have the same character," she said.

North Korea has a standing army of about 1.2 million, with millions more in reserve, and a supply of missiles capable of reaching Asian cities. North and South Korea technically are still at war more than 50 years after the Korean conflict ended.