US President Barack Obama spoke with South Korean President Lee Myung-Bak on Monday and the two vowed to work closely toward ending North Korea's nuclear weapons programmes, the White House said.
The two "discussed North Korea and agreed to work closely as allies and through the six-party talks to achieve the verifiable elimination of North Korea's nuclear weapons and programmes", spokesman Robert Gibbs said in a statement.
"In a warm and substantive talk, the president conveyed his deep commitment to the United States-Republic of Korea alliance. Both presidents expressed their intention to expand co-operation on global issues," Gibbs added.
The pair also "discussed the current financial crisis and agreed to work together, including at the G-20 Summit in London, to stabilise the global economy, to spur growth, and to get credit markets flowing".
A six-nation deal signed in February 2007 offers the North energy aid, normalised ties with Washington and Tokyo and a permanent peace pact if it dismantles its atomic plants and hands over all nuclear weapons and material.
But the disarmament talks are stalled by disagreements over how the North's declared nuclear activities should be verified.
Earlier on Monday, North Korea's military vowed to keep atomic weapons until the United States removes its nuclear threat, reiterating its tough stance.
"The DPRK [North Korea] will never 'dismantle its nuclear weapons' unless nukes in South Korea are dismantled to remove the nuclear threat from the US," a spokesman for the North's General Chiefs of Staff was quoted as saying by the official Korea Central News Agency.
South Korea denies having any atomic weapons.