Lee Jae-oh, a close ally of former President Lee Myung-bak, joined an already crowded field of conservative presidential candidates on Monday.

The former five-term lawmaker declared his presidential bid unveiling a series of reform pledges, including reshaping South Korea's government structure criticized for giving inordinate power to a single national leader.

Lee, a co-chair of the minor conservative Ever-Green Korea Party and outspoken critic of former President Park Geun-hye, said he would complete his reform plans "within one year" if elected president and voluntarily step down.

"I will resign one year after my inauguration (as president) after having completed five reform tasks, including a constitutional revision to enact a power-sharing model," Lee said during a meeting with members of the nascent party.

Lee was referring to the government model in which a prime minister, elected by the National Assembly, is given more power and leads internal affairs such as the economy, while the role of a president is limited to handling external affairs such as defense and foreign affairs.

Along with the power-sharing model, Lee pledged to introduce a four-year, double term presidency. Currently, a South Korean president can serve for a single five-year term.

His reform pledges included altering the parliamentary election system from the current single-seat constituency to a multiple-number system, which would weaken the domination of major parties and facilitate smaller parties' advance into the National Assembly.

He also promised to clinch a peace treaty with North Korea through a new dialogue channel and pursuing the construction of three express train routes linking South and North Korea all the way to Europe.

Lee launched the new party in January, vowing to push for reforms to remove political corruption and establish a "fair and just" society. (Yonhap)