South Korean President Park Geun-hye says President Barack Obama's vision of a world without nuclear weapons must start on the Korean peninsula, where the South lives in fear of a nuclear attack from the north.
President Park addressed a joint meeting of the U.S. Congress on Wednesday in Washington.
"The republic of Korea will never accept a nuclear-armed North Korea," said President Park.
She thanked Congress for American support, calling the countries' friendship "second to none" as they work to improve their economies and create a path toward reunifying the Korean peninsula.
She said this path to peace and unity starts with trust, but noted that, as they say in North Korea, "it takes two hands to clap."
"The pattern is all too familiar and badly misguided. North Korea provokes a crisis, the international community imposes a certain period of sanctions, later it tries to patch things up by offering concessions and rewards. Meanwhile, Pyongyang uses that time to advance its nuclear capabilities, and uncertainty prevails. It is time we put an end to this vicious circle," she said.
President Park is on a five-day U.S. visit, which began Monday at the United Nations.
After meeting Tuesday with President Obama at the White House, Park said Seoul and Washington must not tolerate North Korea's recent wave of threats.
President Obama said the United States is ready to engage diplomatically with the North if it decides to embrace a "peaceful path."
But he said the days when North Korea could create a crisis and elicit concessions are "over," calling the United States and South Korea "as united as ever" and North Korea "more isolated than ever."
The South Korean leader is heading a delegation of more than 50 South Korean business leaders and will stop Thursday in Los Angeles to meet with Korean entrepreneurs.
The trip is meant to send a strong message of unity to the North, which has gradually reduced the intensity of its war rhetoric, following weeks of threats of nuclear and conventional attacks against the United States and South Korea.