South Korea's president says North Korea must abandon efforts to build nuclear weapons. The demand comes as Pyongyang announced it is scrapping an agreement to keep the Korean Peninsula nuclear free. The U.S. military also has confirmed that North Korea has targeted U.S. aircraft with lasers.

President Roh Moo-hyun said Pyongyang's pursuit of nuclear weapons will determine if relations between the two Koreas improve.

Mr. Roh, in a speech while visiting New York, called on North Korea to give up its nuclear weapons programs and re-admit international nuclear inspectors. The president said North Korea has a choice of going "down a blind alley or it can open up."

The trip is Mr. Roh's first overseas since taking office in February. He meets with President George W. Bush in Washington on Wednesday, to discuss their governments' differences in responding to North Korea's quest to obtain nuclear weapons.

South Korea favors a more conciliatory approach to North Korea than the Bush administration has taken so far. Both governments, however, stress they want the issue resolved peacefully.

North Korea's official news agency said an 11-year-old declaration between North and South Korea to keep their countries free of nuclear weapons is a "dead document." It was the North's last international agreement to remain nuclear free.

South Korean officials said the statement might be a negotiating ploy following talks last month in Beijing with U.S. officials. During that meeting, North Korean delegates reportedly admitted their country has nuclear bombs.

North Korea expert Tim Savage said Pyongyang's rejection of the agreement comes as no surprise. "This is the same game that has been played out for months. The North Koreans keep trying to up the ante to force the U.S. to the negotiating table. The Bush administration continues to refuse to engage in any serious dialogue," Mr. Savage said.

On Tuesday, the U.S. military confirmed that North Korea directed lasers at U.S. aircraft on a training flight along the heavily fortified frontier.

A U.S. military spokeswoman in Seoul said two pilots reported in March that laser-detecting systems showed their aircraft had been targeted by lasers. Neither aircraft was damaged and the pilots landed safely. She said the North has targeted U.S. planes with lasers occasionally in the past.

Last October, the United States said North Korea admitted having a secret nuclear weapons program, in violation of its international commitments. Tensions have risen since then, as Pyongyang pulled out of the global Non-proliferation Treaty and scrapped a 1994 agreement with the United States to give up its nuclear weapons programs in return for energy aid.