Foreign Minister Taro Kono on Saturday suggested there are signs North Korea is preparing to hold another nuclear test even as tensions on the Korean Peninsula ease ahead of a rare summit between the two Koreas.

The North appears to be “working hard to get ready for the next nuclear test,” Kono said in a lecture in Kochi, referring to the removal of soil from a tunnel at a site where past tests were conducted.

His remarks might be based on satellite imagery provided by the United States.

As for the possibility of summit talks taking place between Prime Minister Shinzo Abe and North Korean leader Kim Jong Un, Kono expressed caution about reacting hastily to Pyongyang’s charm offensive.

“There’s absolutely no need to rush things,” the top diplomat said, adding that North Korea may take advantage of countries accepting invitations to send their leaders to Pyongyang for talks.

There are signs of a thaw on the divided peninsula, with global attention fixed on two closely related events — an inter-Korean leaders’ summit scheduled for April 27, and an unprecedented U.S.-North Korea summit that is expected to be held by the end of May.

North Korea’s most recent nuclear test, its sixth and most powerful, was conducted in September 2017.