The prosecution will summon and question former presidential secretary for policy coordination Ahn Jong-beom on Wednesday over the Choi Soon-sil scandal.
Ahn is a key figure involved in mounting corruption allegations surrounding Choi. He is suspected of serving as a link between the presidential office and the president's longtime confidante.
The ex-presidential secretary is believed to have been deeply involved in setting up and raising funds for two nonprofit foundations � Mir and K-Sports.
He is also suspected of having supported the business of Choi's controversial company The Blue K.
The prosecution placed a travel ban on Ahn on Monday.
Source: KBS World Radio