Won Sei-hoon saw opposition figures as North Korean sympathisers and instructed senior National Intelligence Service officials to prevent them from gaining support on the Internet ahead of elections, the Seoul Central District Prosecutors' Office said in a statement.
Under his order, NIS expanded its "psychological warfare" squads and its agents posted comments criticising liberal candidates and praising conservative Park Geun-hye, prosecutors said. NIS agents tried to portray opposition candidate Moon Jae-in as too soft on North Korea and unqualified to protect South Korea against North Korean threats, prosecutors said.
The indictment adds to troubles for the spy agency, which has been criticised in recent years for failing to have timely intelligence about North Korea.
Won resigned as National Intelligence Service chief in March after serving four years under conservative President Lee Myung-bak. Prosecution officials raided NIS in Seoul in late April.
More From This Section
NIS wouldn't comment on the allegations, and said it will seek a fair ruling in a coming trial.
Under a law governing the agency, Won would face up to five years' imprisonment if found guilty.