North Korea fired off at least eight short-range ballistic missiles into the Sea of Japan on Sunday, according to the South Korean military, in a barrage of launches that some analysts characterized as unprecedented.

The launches were the latest signal by North Korean leader Kim Jong Un that he intends to double down on his nuclear and missile programs despite crushing sanctions and an apparent COVID-19 crisis gripping his country.

The South Korean military said the launches had come from areas around Sunan in Pyongyang; Kaechon, north of the capital; the northwestern region of Tongchang-ri; and the eastern city of Hamhung, the Yonhap news agency reported. Seoul said the missiles had flown 110 to 670 kilometers at altitudes of 25 to 90 kilometers, with speeds between mach 3 and 6.