A former chief of staff to South Korean President Lee Myung-bak declared himself a presidential candidate Tuesday, joining the ranks of ruling party heavyweights vying for the nation's top office.

Yim Tae-hee, a former three-term lawmaker of the ruling Saenuri Party who also served as labor minister in the Lee administration, said during a press conference he will dismantle the political establishment beset by regional and factional feuds.

He also directly confronted interim Saenuri chairwoman Park Geun-hye, the unrivaled presidential front-runner on the conservative ticket for the December poll.

"(Park should) play a role in demolishing the old political framework of the past 40 years," Yim said, stressing political necessity for her role as a "kingmaker."

The 56-year-old's remarks are seen as a call on Park to step aside and help other ruling party candidates replace Lee, whose single five-year term ends in February 2013.

Other Saenuri contenders include Gyeonggi Governor Kim Moon-soo, billionaire lawmaker Chung Mong-joon and former special affairs minister Lee Jae-oh.

They have demanded the ruling party change its primary rules so that moderates and young voters will take greater part in the party's presidential nomination race, a challenge to Park. They all lag far behind Park in opinion polls.