U.S. Ambassador to the United Nations Samantha Power is visiting South Korea amid rising concern over North Korea's nuclear program and worries about increasing sophistication of the North's missiles.


Ambassador Samantha Power visited the South Korean side of the Demilitarized Zone and toured the line that separates the two Koreas. Her visit comes as analysis of satellite images suggests Pyongyang may soon test an intercontinental ballistic missile.


Power told a news conference in Seoul the United States will use all available means to isolate the regime in Pyongyang.


"We are committed to using all the tools in our toolkit to address the serious threat, including diplomatic pressures we are mobilizing around the world to convince other nations to isolate the regime."


Power met with South Korean Prime Minister Hwang Kyo-ahn to discuss North Korea's nuclear program. She emphasized the close ties between the United States and its ally on the Korean peninsula.


"While the United States may be farther away geographically from the DPRK than you are, we take the threat that the DPRK poses just as seriously. We understand that this is not only a threat to the United States and the Republic of Korea, but to the very foundation of our international order."


The United States and South Korea have urged governments around the world to take action against North Korea. Reports say they are applying pressure to stop North Korea from sending guest workers overseas to earn money for the regime.


There are also calls for tougher U.N. Security Council sanctions after the North's fifth nuclear test last month in defiance of U.N. sanctions.