Amid a disturbing rise in belligerent rhetoric from the North toward the South and signs it may be getting ready to test-fire a ballistic missile, she urged Pyongyang to halt "provocative and unhelpful" gestures and rejoin stalled six-nation nuclear disarmament talks.
"North Korea is not going to get a different relationship with the United States while insulting and refusing dialogue with (South Korea)," Clinton told reporters at a news conference with South Korean Foreign Minister Yu Myung-hwan.
"We are calling on the government of North Korea to refrain from being provocative and unhelpful in a war of words that it has been engaged in because that is not very fruitful," she said.
Clinton, who also received a military briefing on the situation along the demilitarized zone between North and South Korea and discussed broader issues with South Korean President Lee Myung-Bak, praised Seoul for its democracy and prosperity.
She said that was "in stark contrast to the tyranny and poverty across the border to the North" and commended the "people of South Korea and your leaders for your calm, resolve and determination in the face of provocative and unhelpful statements and actions by the North."
CBS News reporter Don Kirk reported that Clinton promised President Lee the U.S. would work to further develop its relationship with South Korea, and to persuade the North to agree to a "verifiable" nuclear disarmament program.
She declined to comment on intelligence suggesting the North could soon fire a missile but noted such an act would violate U.N. Security Council Resolution 1718, which was passed after Pyongyang detonated a nuclear device in 2006.
"The North should refrain from violating this resolution and also from any and all provocative actions that could harm the six-party talks and aggravate the tensions in the region," Clinton said.
She demanded that the North follow through on promises it made to dismantle and verifiably disable its nuclear weapons program during negotiations with, , , South Korea and the United States last year, saying Washington is not willing to engage with Pyongyang until it does so.
Clinton said the new U.S. special representative for North Korea, Stephen Bosworth, a former U.S. ambassador to South Korea, would work with South Korea, Japan, China and others to look at ways to get Pyongyang back to the negotiating table and deal with broader policy.
Bosworth will also deal with North Korean human rights and humanitarian issues, she said, praising him as "a capable and experienced diplomat" who will report to her and President Barack Obama.
En route to South Korea from Indonesia on Thursday on her first overseas trip as America's top diplomat, Clinton surprised reporters traveling with her when she spoke candidly about a possible succession crisis in North Korea and its impact on restarting the talks.
Those comments marked a rare, if not unprecedented, instance of a senior U.S. official publicly discussing such a diplomatically sensitive matter.
On Friday in Seoul, Clinton again acknowledged concerns over a potential power struggle to replace ailing North Korean leader Kim Jong Il, but she stressed that the United States was still addressing its concerns to the existing government.
North Korean officials have steadfastly denied Kim is ill but state-run media made no mention of Kim's public appearances for weeks last fall, feeding fears that his sudden death without naming a successor could leave a power vacuum and spark an internal struggle.
Kim's father had cultivated a powerful cult of personality that encompassed him and his son, and recent dispatches in North Korea's state-run Korean Central News Agency have stressed the importance of bloodline and inheritance in what is seen as references to the succession plan.
Kim Jong Il is believed to have at least three sons: Kim Jong Nam, in his late 30s; Kim Jong Chul, in his late 20s; and Kim Jong Un, a son in his mid-20s by another companion.
The eldest is believed to have been the favorite to succeed his father until he was caught trying to enter Japan on a fake passport in 2001, reportedly to visit Tokyo Disneyland.
Last month, the South Korean news agency Yonhap said the youngest, Kim Jong Un, was named Kim's heir apparent.
And, on Thursday, citing unidentified sources in Beijing, Yonhap said Kim Jong Un had registered his candidacy for March 8 parliamentary elections in a sign the son is poised to become the country's next leader.
Fueling speculation of possible power struggle, the North's state-run news agency reported last week that Kim Jong Il had replaced his defense minister and chief of the military's general staff.