The former chief of the nation's main intelligence agency was allowed to return home Tuesday after around 14 hours of questioning by prosecutors over allegations that he attempted to influence public opinion ahead of last year's presidential election.

"I sincerely responded to the prosecution's investigation," Won Sei-hoon told reporters as he emerged from the Seoul Central District Prosecutor's Office in southern Seoul past midnight.

Won, who headed the National Intelligence Service (NIS) under former President Lee Myung-bak, is alleged to have sought to sway public opinion in favor of the ruling party candidate ahead of the presidential race in December.

He appeared before the office around 10 a.m. Monday and was grilled over whether he ordered NIS agents to post a slew of politically sensitive comments on the Internet against the opposition candidate, according to prosecutors.

Won reportedly denied the charges against him, claiming that there was nothing illegal about the agency's operations.

After police wrapped up their four-month investigation in March by concluding that two agents had allegedly participated in the illegal political activities, the prosecution immediately launched a task force to look into suspicions that the agency had extensively and systemically intervened in the presidential election.

Won, who has been barred from leaving the country pending investigation since last month, is expected to be summoned again for further questioning, prosecutors said. (Yonhap News)