The joint announcement Wednesday by the two nations comes little more than two months after the death of longtime ruler Kim Jong Il, and suggests North Korea has met the key U.S. preconditions for restarting multi-nation disarmament-for-aid talks that the North withdrew from in 2009.
Secretary of State Hillary Rodham Clinton called North Korea suspension of nuclear activities a "modest first step" but also "a reminder that the world is transforming around us."
She told a Senate hearing that the North has agreed to a moratorium on nuclear activities at Yongbyon, including uranium enrichment activities, and will allow International Atomic Energy inspectors to verify and monitor it, and to confirm disablement of its nuclear reactor and associate facilities.
Since 2006 North Korea has tested missiles, staged two nuclear tests and unveiled a uranium enrichment program that could give it a second route to manufacture nuclear weapons, in addition to its existing plutonium-based program. At low levels, uranium can be used in power reactors, but at higher levels it can be used in nuclear bombs.
Clinton said the United States will meet with North Korea to finalize details for a proposed package of 240,000 metric tons of food aid, referring to it as "nutritional assistance." She said intensive monitoring of the aid would be required.
North Korea, which appealed for the aid a year ago to alleviate chronic food shortages, issued a similar, although differently worded statement released simultaneously in Pyongyang.
An unidentified spokesman from North Korea's Foreign Ministry said in its statement carried by the state-run news agency that the North agreed to the nuclear moratoriums and the allowance of U.N. inspectors "with a view to maintaining positive atmosphere" for the U.S.-North Korea talks.
The U.S. still has nearly 30,000 troops based in South Korea, a legacy of the 1950-53 Korean War, that ended in a armistice rather than a peace treaty.
Wednesday's announcement follows talks in Beijing last week between U.S. and North Korean negotiators, the first since negotiations were suspended after Kim's death in December from a heart attack.
Before his death, the U.S. and North Korea were close to such an agreement, which appears to meets U.S. preconditions for restarting the six-nation talks suspended three years ago. The talks also include China, Japan, Russia and South Korea.
"The United States still has profound concerns but on the occasion of Kim Jong Il's death I said it is our hope that the new leadership will choose to guide their nation on to path of peace by living up it to its obligations," Clinton said.
Clinton said the United States will judge the new regime led by Kim's youngest son, Kim Jong Un, by its actions.
The U.S. said it had no hostile intent toward North Korea and was prepared to increase people-to-people exchanges, including in the areas of culture, education, and sports.
North Korea's willingness to agree to the moratoriums and allow in U.N. inspectors is a major sign of the country's intentions in the early days of the rule Kim Jong Un, who is believed to be in his late 20s.
Kim Jong Un's consolidation of power, with the help of a group of senior advisers who worked with his father and grandfather, appears to be going smoothly. But outsiders have been closely watching to see how Kim handles nuclear diplomacy with the United States and delicate relations with rival South Korea.
Despite Wednesday's progress, many observers are skeptical whether North Korea will ever give up its nuclear program. Since Kim Jong Il's Dec. 17 death, North Korea has vowed to maintain the late leader's policies and has linked its nuclear program to Kim's legacy.
"North Korea uses (the nuclear program) as leverage to win concessions in return for disarmament measures. Since Kim Jong Il's death, it has called (the program) the country's most important achievement," Baek Seung-joo, an analyst at the state-run Korea Institute for Defense Analyses in South Korea, said. "There is still a long way to go."
There were some differences in the U.S. and North Korean statements on the nuclear moratoriums.
The U.S. said North Korea has agreed to a moratorium on "nuclear activities" at Yongbyon, including uranium enrichment, while the North Korean statement only refers to uranium enrichment. It was not immediately clear if that implied the plutonium-based program would remain.
The North said that the United States made clear that its sanctions against the North "are not targeting the civilian sector, including the livelihood of people" and that once six-nation nuclear talks are resumed, "priority will be given to the discussion of issues concerning the lifting of sanctions on the (North) and provision of light water reactors."
Although the North has conducted two nuclear tests and has developed a battery of ballistic missiles, it says it is constructing its own light water reactor to generate electricity to alleviate chronic power shortages.