A former chief of staff to President Lee Myung-bak announced Monday his intention to run for the top office and demanded a change in how the ruling Saenuri Party selects its candidate for December's presidential election.

Yim Tae-hee, a former three-term lawmaker who worked as chief secretary to Lee in 2010-2011, is the latest ruling party member to reveal presidential ambitions. Three others declared their bids over the past week, and one more is expected to do so in the coming weeks.

All are in addition to the party's chief and No. 1 presidential hopeful Park Geun-hye, with the unexpectedly large number of contenders spawning views a brewing dispute in the party could heat up over whether to change its primary rules, currently seen as favorable to Park.

"I am preparing to run in the presidential election," Yim told Yonhap News Agency by phone, adding he plans to make a formal announcement before mid-May that he will participate in the ruling party's race to choose its presidential candidate.

Yim, 56, said he believes the party should revise its primary rules in a way that helps broaden its support base, claiming the general elections earlier this month showed the party needs greater support from younger voters if it is to win the December vote.

Yim said he will formally demand a change in primary rules when he announces his bid.

Gyeonggi Province Governor Kim Moon-soo, who was the first to announce his presidential bid in the ruling party, wants to change the primary rules, which currently give roughly the same weight to the voices of party members and other citizens.

Kim has called for an "open primary" to select the party's presidential candidate based on the support shown by ordinary citizens, regardless of party membership. Kim claims the current system fails to correctly reflect the views of the people.

Other contenders against Park have also called for an open primary, including Rep. Chung Mong-joon, who announced his presidential bid over the weekend, and Rep. Lee Jae-oh, a close confidant of President Lee, who is expected to declare his candidacy in coming weeks.

Former Incheon Mayor Ahn Sang-soo also announced over the weekend that he will take part in the primary race, but it was unclear whether he will join calls for changing the primary rules.

Park has been negative about the demand for changing the regulations, stating it "makes no sense to adjust game rules to athletes" but that the "athletes" should adjust to the game rules.

The current rules are believed to be favorable to Park as she has broad support within the party. Park consolidated her standing as a leading presidential hopeful of the party after rebuilding the once-beleaguered party and leading it to a widely unexpected victory in the general elections. (Yonhap News)