Multiple Japanese media outlets say North Korea appears to be preparing for a nuclear test.

Kyodo News cited an unnamed Japanese official as saying that satellite imagery shows tunneling being done at the North’s nuclear testing site in Gilju County, North Hamgyeong Province. The official was cited as saying that the tunneling activity appears to be part of preparations to test a nuclear device.

Earlier the Sankei Shimbun daily, also citing satellite imagery, reported that Pyongyang is tunneling at the site in Gilju and that it is likely preparing to conduct a third nuclear test.