US President Barack Obama has spoken to South Korean President Lee Myung-bak about North Korea's nuclear test and agreed to work with the UN Security Council to address it.
They agreed to work closely together, including at the United Nations Security Council, to seek a range of measures aimed at impeding North Korea's nuclear and ballistic missile programs and reducing the risk of proliferation.
President Obama unequivocally reaffirmed that the United States remains steadfast in its defense commitments to the Republic of Korea, including the extended deterrence offered by the US nuclear umbrella.
Welcome to a more dangerous world, welcome to a world with a new nuclear power and to a world where the global powers are threatened.
Testing nuclear weapons is North Korea's way of saying we can defend ourselves, you have to take us seriously.