North Korea ? A team of U.S. experts has begun disabling North Korea’s nuclear weapons-making facilities, a U.S. official said, the first time Pyongyang has ever moved to scale back its development of atomic bombs.

U.S. State Department spokesman Tom Casey told reporters Monday in Washington that the disabling of the North’s nuclear reactor at Yongbyon “is a positive first step in this process, and we certainly hope to see it continue.”

He had no details about what specific steps the team was conducting.

The North shut down Yongbyon in July and promised to disable it by year’s end in exchange for energy aid and political concessions from other members of talks on its nuclear program: the U.S., China, Japan, South Korea and Russia.