BEIJING (Kyodo) -- A U.S. nuclear weapons expert has released satellite images of what is believed to be a new uranium enrichment facility under construction in Yongbyon in North Korea's northwest, likely the same location flagged earlier this week by the chief of the International Atomic Energy Agency.

The image posted online by Jeffrey Lewis, a professor at the Middlebury Institute of International Studies at Monterey, was taken in April.

IAEA Director General Rafael Grossi told the organization's board of governors on Monday in Vienna that the nuclear watchdog is monitoring the construction of the new structure, which he said has similar features to an existing uranium enrichment plant in Kangson near Pyongyang.

However, Grossi did not provide images of the facility. The new building is located some 2 kilometers away from the existing Yongbyon complex, according to the satellite image.

The new facility has a central hall approximately 95 meters long and 24 meters wide where centrifuges could be installed. It is surrounded by office and support spaces, Lewis said.

Comparing it with a satellite image taken in 2002 during the construction of the Kangson enrichment facility, he noted the similarities in layout and dimensions.

The professor also said North Korea packed more centrifuges into a much smaller floor space as it expanded its production of enriched uranium.

North Korean leader Kim Jong Un toured a nuclear material production base and the Nuclear Weapons Institute last September and in January, according to the country's state-run media. The reports did not disclose the location of the sites.

In an unusual move, the official Korean Central News Agency published pictures in September and January showing arrays of centrifuges at one or more undeclared facilities visited by Kim.

Lewis said Kim probably visited the Kangson plant in September and the Yongbyon facility in January. However, some Japanese researchers have pointed out the leader traveled to the Yongbyon complex twice.