(CNN)-- U.S. Secretary of State Hillary Clinton said Thursday that North Korea's new leader, Kim Jung Un, "has a choice to make" -- become a "transformative leader" or continue the Communist nation's existing policies, which she predicted would lead to its demise.
"He can continue the model of the past and eventually North Korea will change, because at some point people cannot live under such oppressive conditions -- starving to death, being put into gulags and having their basic human rights denied," she said.
"We are hoping that he will chart a different course for his people."
The 29-year-old Kim Jong Un became North Korea's most powerful figure about six months ago, following the death of his father Kim Jong Il. He has only made two public speeches since rising to power -- the first coming at a ceremony marking the 100th anniversary of the birth of North Korea's founder and his grandfather Kim Il Sung, and more recently in June in a speech to about 20,000 children.
Referring to Kim Jong Un, Clinton expressed "hope that the new leadership in Pyongyang will live up to its agreements, will not engage in threats and provocations (and) will put the North Korean people first."
"Rather than spending money on implements of war, feed your people, provide education and health care, and lift your people out of poverty and isolation," she advised North Korea's new leader.
The comments followed a meeting in Washington -- referred to by both sides as the "2-plus-2" talks -- involving Clinton, U.S. Defense Secretary Leon Panetta and South Korea's foreign and defense ministers.
Afterward, the United States and South Korea released a joint statement reaffirming their cooperation on security matters, an alliance they called "a linchpin of stability, security, and prosperity in the Asia-Pacific region and increasingly around the world."
That cooperation was evident in crisis management and "intelligence sharing" before, during and after North Korea's failed long-range rocket launch in April, South Korean Defense Minister Kim Kwan-jin said Thursday. Some expressed concerns that launch, which the U.N. Security Council condemned as a "serious violation" of previous council resolutions, might signal Pyongyang's intentions to fire nuclear weapons on its foes.
Foreign Minister Kim Sung Hwan promised that South Korea and the United States "will show a decisive response" if North Korea moves to "provoke again." Yet he also opened the door for talks.
"The road to dialogue and cooperation is open should North Korea stop its provocation," he said.
A few years after the Korean peninsula was divided after World War II, U.S. forces joined South Korea in the Korean War -- a conflict that ended in a cease-fire, but no peace treaty. North Korea's nuclear weapons capabilities have further heightened tensions in recent years.
This week's meeting in Washington showed the strength of the partnership between two of North Korea's staunchest foes.
In addition to a continued focus on Pyongyang's nuclear and missile programs, the two parties announced a joint defense initiative focused on "evolving threats, such as in space, the maritime domain, and cyberspace," according to the joint statement.
"Working together, we can improve the security of our government, military and commercial infrastructure and better protect against cyber attacks," Clinton said.