WASHINGTON — A U.S. institute monitoring North Korea on Monday questioned Japanese Foreign Minister Taro Kono’s recent remark that there are signs Pyongyang is preparing to conduct another nuclear test.

“Commercial satellite imagery from March 23 shows quite a different picture: namely, that activity at the test site has been significantly reduced compared to previous months,” the U.S.-Korea Institute of Johns Hopkins University said on its 38 North website.

Speaking in the western Japan city of Kochi on Saturday, Kono said North Korea appears to be “working hard to get ready for the next nuclear test,” referring to soil removal from the tunnel at the site where past nuclear tests were conducted.

The institute also said tunneling at the West Portal, a site not associated with any of North Korea’s previous tests, had been active earlier this year but that activity “has slowed down significantly as has other personnel and vehicular movement around the site.”

North Korea last conducted a nuclear test, its sixth and most powerful, in September 2017.