South Korea's new president said Monday that he will never condone North Korea's (searchnuclear development, but a defiant North said its 1992 nuclear-free agreement with South Korea was nullified.

Roh Moo-hyun (search), who visited the Stock Exchange, the World Trade Center site and the United Nations, said Seoul and Washington agree the nuclear standoff with the North must be solved peacefully "by all means."

"North Korea has two alternatives: it can go down a blind alley or it can open up," Roh said at a dinner hosted by the New York-based Korea Society.

"It is incumbent upon Pyongyang to give up its nuclear project and come forward as a responsible member of the international community," he said. "When the North takes this route, the Republic of Korea and the international community will extend the necessary support and cooperation."

When Roh reached the site where terrorists crashed airliners into the twin towers on Sept. 11, 2001, he laid a bouquet of flowers next to a viewing platform where other memorial flowers and trinkets had been left.

"I came here today with the heart of all the Koreans who expressed their condolences ... and I would like to applaud the courage of the American people who overcame the tragedy," Roh said through an interpreter.

New York Mayor Michael Bloomberg (search) told Roh: "Korea has fought wars and has an enemy right across the border that you can look at. America does not. This is a very strange thing for us."

Roh's visit to the stock exchange tied in with a key goal of his mission on the United States: to solidify the trade alliance with the United States, and reassure foreign investors that South Korea is a stable place to do business despite the North Korean nuclear standoff.

The United States is Korea's largest export market, and Korea is the sixth-largest market for U.S. exports.

On Monday, North Korea said a 1992 agreement with South Korea to keep the Korean Peninsula free of nuclear weapons was nullified, citing a "sinister" U.S. agenda.

The statement came amid concern over North Korea's suspected development of nuclear weapons and was the last remaining legal obligation under which North Korea was banned from developing atomic arms. In January, Pyongyang withdrew from the Nuclear Nonproliferation Treaty, a global accord to prevent the spread of nuclear weapons.

"The joint (inter-Korean) agreement to keep the Korean Peninsula nuclear free was nullified because of a sinister and hostile U.S. policy against North Korea," the North's official news agency KCNA said. The statement was monitored by South Korean news agency Yonhap.

The two Koreas signed the agreement in January 1992, pledging to renounce hostilities and ban the development and deployment of nuclear weapons on the divided peninsula.

Later Monday, Roh met with U.N. Secretary-General Kofi Annan and took a tour of the U.N. headquarters in Manhattan. He did not speak to reporters.

"The secretary-general said he would press ahead on humanitarian assistance, and eventually development assistance, to the DPRK," said a statement from Annan's office. DPRK stands for the Democratic People's Republic of Korea, as North Korea is known.

Roh and President Bush planned to meet in Washington on Wednesday to discuss how to find a peaceful solution to the impasse over North Korea's nuclear ambitions.