The 4-member delegation of the U.N. nuclear watchdog left Pyongyang Thursday to the nuclear reactor in Yongbyon, about 100 kilometers northeast of the capital, the Xinhua news agency reported in the capital of North Korea.
"We are going to see the facilities and continue our discussion in more details," Xinhua quoted Olli Heinonen, the head of the delegation of the International Atomic Energy Agency (IAEA), as saying.
Friday afternoon, they are to return to the North Korean capital, where they have been since Tuesday on their five-day trip.
It is the IAEA's first visit to the North since late 2002 when the country expelled its nuclear inspectors and later withdrew from the nuclear Non-Proliferation Treaty.
The visit to Yongbyon came just hours after the United States said that it was "deeply troubled" by the missile launches upon confirming North Korea's Wednesday test-fires of "several missiles," the AFP said.