South Korean prosecutors have indicted a former spy chief on charges of meddling in last year's presidential elections by ordering an online smear campaign against opposition candidates.

The Seoul Central District Prosecutors' Office said Friday that Won Sei-hoon ordered his agents to post comments slandering liberal candidates and praising conservative Park Geun-hye. Park won the December vote and took office in February.

Won resigned as National Intelligence Service chief in March after serving for four years under former President Lee Myung-bak.

Prosecutors say in a statement that NIS also tried to portray opposition candidate Moon Jae-in as a North Korea sympathizer. NIS plans to issue its response later.

Won would face up to five years' imprisonment if found guilty. The opposition threatens to impeach the justice minister over the scandal.