North Korea has hardened its stance on disarmament, saying it has "weaponized" plutonium into warheads, but hopes for better ties with U.S. President Barack Obama, a U.S. researcher who visited the North said Jan. 17.

Officials say the weapons cannot be inspected and Pyongyang might keep them even if it normalizes relations with Washington, said Selig Harrison, director of the Washington-based Center for International Policy's Asia program.

Harrison, who has visited the North 11 times since 1972, said he met recently with the North's nuclear envoy, Ri Gun, and other officials.

The officials said, "North Korea is now a nuclear weapons state and will not commit itself now on when it will give them up as a result of denuclearization negotiations," Harrison told reporters in Beijing. "We are not in a position to say when we will abandon nuclear weapons," he quoted Ri as saying.