South Korea's former first lady Kim Keon Hee has been arrested after a court late on Tuesday issued a warrant to arrest her following accusations of graft that she denies, a special prosecutor leading a wide-reaching probe said.

Kim is South Korea's only former first lady to be arrested, joining her husband, ex-President Yoon Suk Yeol, in jail as he faces trial following his ouster in April over a botched bid to impose martial law in December.

Earlier in the day, Kim, wearing a black suit, bowed as she arrived at court, but did not answer reporters' questions or make a statement. After the hearing ended she left to await the ruling at a detention center in Seoul, the capital, in line with customary practice.