Washington's decision to lift sanctions and remove the North from a terrorism list came in a weekend meeting with North Korean representatives in Geneva, the spokesman said in comments carried by the North's official Korean Central News Agency. In line with KCNA practice, the spokesman was not identified.
Nancy Beck, a spokeswoman of the U.S. State Department in Washington said she did not have confirmation of the KCNA report.
The move came after North Korea agreed to take "practical measures to neutralize the existing nuclear facilities" this year, the spokesman said.
U.S. chief nuclear negotiator Christopher Hill said Sunday in Geneva that North Korea agreed in talks held in the Swiss city to declare and disable its nuclear programs by the end of this year.
Hill said it was the first time the North has set a timeline for declaring and disabling its nuclear programs since the February deal in which Pyongyang pledged to shut down its nuclear reactor, disclose its nuclear programs and disable related facilities in exchange for economic and political concessions.
Kim Kye Gwan, the North's top nuclear envoy, said separately he had shown willingness to declare and dismantle all nuclear facilities, but he mentioned no dates.
Hill apparently said nothing publicly in Geneva, however, about the terrorism issue.
Besides being subject to economic sanctions, North Korea has also been on a U.S. list of states that sponsor terrorism, effectively blocking the North from being able to obtain low-interest loans from international lending agencies like the World Bank and the International Monetary Fund.
The North was first put on the list for its alleged involvement in the 1987 bombing of a South Korean airliner that killed all 115 people aboard.
South Korean presidential spokesman Cheon Ho-seon also hailed the Geneva agreement, calling it "a good signal" for a process to bring peace to the divided Koreas.
Cheon also said at a press conference Monday that he expected the North to honor its commitment to declare and disable its nuclear programs by the end of this year as promised.
The U.S. gesture improves the prospects for the diplomatic normalization between the two sides as well as the next round of nuclear talks involving the two Koreas, the U.S., China, Russia and Japan, a South Korean expert on North Korea said.
The agreement "is a very important breakthrough," said Paik Hak-soon, of the Sejong Institute, a security think-tank, outside Seoul.
"Any obstacles to the normalization of ties between North Korea and the U.S. will be cleared if the two sides follow through on their parts of the deal on the principle of simultaneous action," Paik said.
The two sides have held a series of bilateral talks aimed at moving toward full diplomatic relations as part of a February disarmament deal.
The nuclear accord also mandates the U.S. to begin the process of delisting the North as a terrorism sponsor and advance the process of terminating the application of the Trading with the Enemy Act with respect with the North.
South Korea's Foreign Minister Song Min-soon hailed the meeting in Geneva as "very positive" but issued a note of caution about the prospect of disabling North Korea's existing facilities.
"We have to be careful with these new developments but at the same time also make sure that we move forward," Song said.
In Tokyo, newly appointed Foreign Minister Nobutaka Machimura expressed cautious optimism, saying the fact that positive discussions had taken place was "a very good way" for the six-party talks to make progress.