The state spy agency used automated messaging programs to spread large numbers of online posts favoring the ruling party ahead of last year's parliamentary and presidential elections, opposition lawmakers claimed Wednesday.

The claim comes amid snowballing allegations that the National Intelligence Service (NIS) and other government bodies conducted an online smear campaign against the main opposition party in a bid to sway public opinion in favor of the ruling party in last year's polls.

Former NIS chief Won Sei-hoon is on trial on charges of ordering the smear campaign.

Two weeks ago, the prosecution asked the Seoul Central District Court to allow it to rewrite Won's indictment with additional charges of election meddling. Prosecutors claimed that the spy agency had posted more than 1.2 million Twitter messages in favor of the ruling party ahead of both the April 2012 parliamentary elections and the December presidential vote.

Opposition lawmakers on the National Assembly's legislative and judiciary committee said they analyzed the details of the additional charges and found evidence of "systematic election interference."

They also claimed that the NIS used automated messaging programs such as Twitterfeed and TweetDeck to simultaneously spread large numbers of messages posted on far-right websites, blogs and Twitter groups.

"General news sites publish hundreds of various pieces per day, making it difficult to filter them with automated programs, so (the NIS) connected only to far-right sites," Rep. Lee Choon-suk of the main opposition Democratic Party said in a joint press conference.

"The (sites) were full of unrefined profanity, unconfirmed false information, and posts dividing the public into the left and right." (Yonhap News)