The U.S. diplomat also said North Korea had made no explicit promises that it would conduct no further nuclear weapons tests. And he said the UN Security Council resolution on North Korea remained in force.
China's Foreign Ministry announced earlier that Pyongyang agreed to rejoin six-party talks after the chief envoys to the negotiations from China, North Korea, and the United States held an informal meeting in Beijing.
The talks also include South Korea, Japan, and Russia.
Russia and South Korea's Foreign ministries have both welcomed Pyongyang's decision to return to negotiations.
But Japanese Foreign Minister Taro Aso said Tokyo opposes North Korea's return to six-party talks unless it renounces nuclear weapons.
(Reuters, AFP, AP)