"I, Ahn Cheol-soo, will become not a president of the conservatives nor of the liberals, but a president of all the people of the Republic of Korea," he said in Gwanghwamun Square, the venue of more than five months of protests that led to the ouster of former President Park Geun-hye.

"Now is the time to talk about the future. The future is already in our midst. The upcoming presidential election will be an election to choose the future of the Republic of Korea."

The former software mogul reiterated his pledge to end the "worn" politics of vested rights, ideological and regional division, confrontation and factional feuds.

He also took a swipe at his rivals, saying most of them were at the center of political power in past administrations.

Moon Jae-in, the front-runner and candidate of the liberal Democratic Party, was chief aide to former President Roh Moo-hyun, Hong Joon-pyo of the former ruling conservative Liberty Korea Party was previously party chairman, while Yoo Seong-min of the splinter conservative Bareun Party was floor leader of the Liberty Korea Party's predecessor.

"They all played important roles in the ruling party or the government," Ahn said. "But the North Korean nuclear and missile crisis has only grown. The Republic of Korea is seized by a national security crisis and diplomatic anxieties, and the economic crisis is heading toward its worst."

Ahn claimed that if he takes power, he will immediately begin reforms in politics, the prosecution and the economy and launch talks for a constitutional revision.

He has recently ranked second in opinion surveys behind Moon, although their gap has begun to grow. (Yonhap)