TOKYO (AFP) - Japanese Prime Minister Naoto Kan on Friday stepped down as president of the ruling party, paving the way for the selection of the disaster-hit nation's sixth new premier in five years. Kan's resignation comes after nearly 15 turbulent months in power during which his response to the March 11 earthquake, tsunami and resulting nuclear plant accident drew fierce criticism and sent his approval ratings plummeting. "I propose to you that I resign as the leader of the Democratic Party of Japan today," Kan told party lawmakers on Friday. "Once a new leader is elected, I will resign promptly as prime minister and my cabinet will resign." A leadership election for a new party president, who would then become prime minister, is expected on Monday. Parliament will then vote the leader in as premier on Tuesday. On his time leading Japan during its worst post-war crisis, Kan said: "I believe I did my best and did what I had to do in severe conditions." But he acknowledged at a later press conference: "I was not sufficiently competent and prepared as the nuclear accident in Fukushima could not be prevented in advance." After surviving a no-confidence vote in June, Kan said he would quit on condition that three key bills were passed - a second budget, a budget financing bill and legislation promoting the use of renewable energy. The budget for reconstruction in quake-hit areas was approved in July, while the final two bills were passed Friday, clearing the way for him to depart. At least five candidates are jockeying to succeed Kan, including former foreign minister Seiji Maehara, Finance Minister Yoshihiko Noda and fiscal policy minister Banri Kaieda. The winner faces the unenviable task of overseeing Japan's biggest post-war reconstruction, resolving the world's worst nuclear crisis since Chernobyl 25 years ago, and shielding the economy from a soaring yen.