Japan's beleaguered¹ Prime Minister Naoto Kan has announced his resignation, clearing the way for the country's sixth leader in five years.

四面楚歌的日本首相菅直人宣布辞职，这是日本五年之内第六任领导。

Mr Kan has been criticised for failing to show leadership after the devastating² 11 March earthquake and tsunami³, and ensuing（接着发生的） nuclear crisis.

In June, Mr Kan pledged to quit if parliament passed three key pieces of legislation, which it did on Friday.

The ruling Democratic Party of Japan will choose a new leader on Monday.

Mr Kan's successor as party head will almost certainly become Japan's next prime minister.

Challenges ahead

Mr Kan announced his decision to stand down（退出） at a DPJ meeting, which was broadcast to the nation. He is expected to give a news conference later on Friday.

Looking back on his 15 months in office, Mr Kan said he had done all he could given the difficulties he faced, including the Fukushima Daiichi nuclear disaster and political infighting（暗斗，混战） - including within his own party.

"Under the severe circumstances, I feel I've done everything that I had to do," he said. "Now I would like to see you choose someone respectable as a new prime minister."

The 64-year-old's resignation had been widely expected, and comes amid tumbling public support.

On 2 June he won a no confidence vote in the Diet (parliament), only by making a promise to step down at a future date.

The Diet passed the final two bills out of three earlier on Friday - one on the budget, the other promoting renewable energy - which he had set as a condition for his departure.

The BBC's Roland Buerk in Tokyo says the new prime minister will have to oversee⁴ the biggest reconstruction⁵ effort in Japan since WWII and resolve the nuclear crisis at Fukushima where reactors⁶ are still leaking radiation.

They will also have to persuade the markets that Japan can overcome a divided parliament to address the biggest national debt in the industrialised world, our correspondent says.