The United States Secretary of State Condoleezza Rice flew into Seoul on Thursday to convince South Korean leaders to back sanctions against North Korea, as a high-powered Chinese delegation urged leaders in Pyongyang to back away from the nuclear brink.
Rice arrived from Tokyo where Japanese leaders assured her of their support for tough trade sanctions imposed by the UN Security Council after North Korea exploded its first nuclear bomb last week.
South Korea in contrast has been reluctant to give up its "sunshine policy" of rapprochement with the isolated communist regime or to take economic actions that could cause the collapse of its impoverished neighbour.
North Korea this week called the sanctions a "declaration of war" and warned of a "merciless" response to anyone who undermines its sovereignty.
Senior US officials said a key message Rice would give South Korean leaders is that Washington will not seek to impose the UN sanctions in a way that would further destabilise the situation.
"We will make clear to the Koreans that the United States has no interest in ratcheting up tensions," said one senior official accompanying her.
The UN resolution bans trade with North Korea related to its development of nuclear arms, ballistic missiles and other weapons of mass destruction, and imposes financial controls to starve the North Korean military of funds.
But the most controversial measure calls for the inspection of cargo to and from North Korea, aimed at preventing its cash-strapped government from selling material for an atomic bomb or other illicit weapons to terrorists.
Rice was due to meet with President Roh Moo-hyun and then hold a trilateral meeting with South Korean Foreign Minister Ban Ki-Moon and his Japanese counterpart Taro Aso -- the first such three-way ministerial encounter in more than a year.
Her visit came amid reports that North Korea could try to test another nuclear weapon, and as a senior US official revealed that a high-powered Chinese delegation was in Pyongyang Thursday in a bid to talk them out of it.
"I'm pretty convinced that the Chinese will have a very strong message about future tests," the official said.
The delegation was also expected to press North Korea to return to six-party negotiations involving China, Japan, Russia, South Korea and the United States.
The six reached an agreement in September 2005 under which North Korea would give up its nuclear program in return for security guarantees and a massive influx of aid.
But Pyongyang walked out of the talks last November to protest US sanctions aimed at locking it out of the international banking system.
The official, speaking on condition of anonymity, said the delegation was led by State Councilor Tang Jiaxuan, a former foreign minister and included "all the foreign ministry's point people on North Korea."
Before going to North Korea, Tang met last week with US President George W. Bush in Washington and Russian leaders in Moscow, though he did not discuss his plans for the Pyongyang trip with US officials.
The outcome of the talks was expected to be discussed when Rice visits Beijing on Friday, but US officials downplayed suggestions of an immediate breakthrough.
China is North Korea's oldest ally and biggest trading partner and has been reluctant to impose sanctions on its neighbor.
But the State Department official said there had been a "dramatic shift" in China's policy since North Korea test-fired a series of ballistic missiles in July and then carried out last week's nuclear test.
"China is very concerned about the development of nuclear weapons on its border, the proliferation of those weapons and the possible transfer of those weapons," he said.
In Seoul, Rice will discuss South Korea's participation in efforts to track and inspect North Korean shipping, aimed at preventing it from trafficking in nuclear materials or weapons of mass destruction, US officials said.
The Americans will also press South Korea to curb or end a huge tourist complex it finances at Mount Kumgang, which provides North Korea with tens of millions of dollars in hard currency each year.
But they cautioned that Rice was unlikely to seek any specific commitments from the South Koreans at this time.