The North Koreans also agreed to a moratorium on long-range missile launches, of particular interest to neighboring Japan and South Korea.
The New York Times said the agreement was part of a deal in which the United States promised to send food to North Korea, which is isolated diplomatically and impoverished.
U.S. officials called the new deal "important, if limited," the Times said. Obama administration officials had suggested a potential breakthrough in what seemed to be an impasse on nuclear arms with North Korea following the death last year of Kim Jong Il, the country's leader. The elder Kim was replaced by one of his sons, Kim Jong Un.
The apparent agreement to allow inspectors from the International Atomic Energy Agency back into North Korea -- they were expelled in 2006 -- appeared to be a significant concession, the Times said.
"These are concrete measures that we consider a positive first step toward complete and verifiable denuclearization of the Korean peninsula in a peaceful manner, which remains this administration's core goal," White House news secretary Jay Carney told reporters. "The agreements that the North Koreans have made are very welcome, but obviously they need to be followed up by actions."
IAEA Director General Yukiya Amano called the announcement "an important step forward."
"As I have said before, the agency has an essential role to play in verifying the DPRK's nuclear program," Amano said in a statement.
"Pending further details, we stand ready to return to Yongbyon to undertake monitoring activities upon request and with the agreement of the agency's board of governors."
The U.S. State Department's announcement did not say when North Korea would fulfill its side of the deal or when talks would resume among North Korea, South Korea, the United States, China, Russia and Japan on North Korean weapons.
"The United States still has profound concerns regarding North Korean behavior across a wide range of areas, but today's announcement reflects important, if limited, progress in addressing some of these," department spokeswoman Victoria Nuland said in a statement.