Welcoming the progress, President Barack Obama's administration said it would move ahead on a long-mulled plan to deliver 240,000 metric tons of food aid to the impoverished state which suffered a major famine in the 1990s.
But the agreement, reached after talks last week in Beijing, is certain to be met with scepticism in many quarters as North Korea has repeatedly agreed to end its nuclear programme only to renounce agreements when tensions rise.
"The United States still has profound concerns regarding North Korean behaviour across a wide range of areas, but today's announcement reflects important, if limited, progress in addressing some of these," State Department spokeswoman Victoria Nuland said in a statement.
Nuland said that North Korea – which has tested two nuclear weapons – has agreed to the return of inspectors from the International Atomic Energy Agency, the UN nuclear watchdog, at its main Yongbyon nuclear facility.
North Korea "has agreed to implement a moratorium on long-range missile launches, nuclear tests and nuclear activities at Yongbyon, including uranium enrichment activities," she said.
The agreement came despite initial US doubts that North Korea would take major decisions after the death in December of veteran leader Kim Jong-il, which put control of the authoritarian state in the hands of untested young son Kim Jong-un.
North Korea kicked out IAEA inspectors in 2009 when it accused the Obama administration of hostility and renounced a previous six-nation agreement to halt its nuclear programme.
Nuland in her statement said that the United States "reaffirms that it does not have hostile intent toward the DPRK and is prepared to take steps to improve our bilateral relationship in the spirit of mutual respect for sovereignty and equality."
Nuland also called for greater people-to-people exchanges with North Korea, known officially as the DPRK or Democratic People's Republic of Korea.