A motorcade carrying South Korea's impeached President Yoon Suk Yeol leaves for Seoul Detention Center at the Corruption Investigation Office for High-ranking Officials (CIO) following his arrest, in Gwacheon, South Korea, January 15, 2025. Yonhap via REUTERS

TOKYO (Kyodo) -- Japan is monitoring developments in South Korea with "particular and grave" concerns, the top government spokesman said Wednesday, following the detention of President Yoon Suk Yeol over his declaration of martial law in December.

A standoff between rival government forces outside the presidential compound in South Korea is a startling development, even for observers used to the country’s famously rough and tumble politics