Kan, 64, saw his approval ratings tumble amid a perceived lack of leadership after the earthquake, tsunami and nuclear crisis

This article is more than 9 years old

This article is more than 9 years old

The Japanese prime minister, Naoto Kan, announced his resignation on Friday amid widespread criticism of his handling of the aftermath of the 11 March tsunami and the crisis at the Fukushima Daiichi nuclear power plant.

But uncertainty grew over the identity of Japan's next leader – the country's seventh in six years – after Ichiro Ozawa, an influential member of the governing Democratic party of Japan [DPJ], indicated he would not support the early favourite, Seiji Maehara.

In a televised speech to party members, Kan said he was confident he had achieved his aims as leader after seeing the final two of three key pieces of legislation pass through the opposition-controlled upper house earlier in the day.

Kan survived a no-confidence vote in June by promising to step down once the bills – which will finance post-disaster reconstruction and promote renewable energy – had been approved.

"Under these severe circumstances I feel I have done everything I had to do," he said. "Now I would like you to choose someone respectable as the new prime minister."

Party MPs will choose his successor as DPJ president on Monday. The victor is almost certain to be approved as prime minister in the DPJ-controlled lower house the following day.

Maehara, who resigned as Kan's foreign minister in early March over a funding scandal, emerged as the front-runner earlier this week, but his fortunes have since receded after he apparently failed to win Ozawa's backing.

Ozawa continues to wield influence over a large bloc of the DPJ's 398 MPs despite his suspension from the party over a funding scandal. He appeared to be waiting for another candidate to emerge, the Yomiuri Shimbun said.

The paper suggested Maehara, a defence hawk who has warned against China's military buildup, would go into Monday's vote minus Ozawa's blessing. "We definitely cannot trust Mr Maehara," the paper quoted an Ozawa ally as saying.

Kan's approval ratings have plummeted amid criticism of the slow pace of the reconstruction effort and his early handling of the nuclear accident. But he will leave office having won widespread public support for his plan to phase out nuclear power – a move most of his potential rivals oppose.

Aside from Maehara the list of possible candidates includes the finance minister, Yoshihiko Noda, and the trade minister, Banri Kaieda.

Whoever succeeds Kan faces a daunting list of challenges: a nuclear cleanup that could take decades, an economy in recession, a surging yen, a public debt twice the size of Japan's economy and soaring health and social security costs.