Prosecutors on Thursday indicted former President Park Geun-hye with additional bribery charges for illegally accepting billions of won from the state spy agency during her term.

The Seoul Central District Prosecutors' Office said it has added new charges of bribery, embezzlement and loss of state funds to its indictment of Park, who is already on trial on 18 charges in connection with a corruption scandal that stripped her of power in May last year.

According to the prosecution, Park received some 3.65 billion won ($3.43 million) from the National Intelligence Service between May 2013 and September 2016. Three former NIS chiefs have told the prosecution that they gave her up to 200 million won every month.

Prosecutors suspect that Choi Soon-sil, Park's longtime friend and confidante at the center of the scandal, was deeply involved in executing the illegal funds.

Park is accused of spending some of the money for private use, such as bills for secret phones she used to contact Choi, maintenance costs for her private residence in southern Seoul and medical treatment. The funds were also used for incentives and bonuses for Park's close aides, they said.

Prosecutors believe that Park delivered some of the money to Choi to help her keep her boutique afloat while she was out of the country in late 2016, when the scandal was ballooning.  

Prosecutors suspect that the money from the NIS was kept in a secret vault in the office of Lee Jae-man, then a senior presidential secretary for general affairs.

Prosecutors sought to question Park in prison twice over the fresh allegations, but she refused to cooperate. (Yonhap)