Japanese Prime Minister Yukio Hatoyama has announced his resignation after just eight months in office.

日本首相鸠山由纪夫宣布辞职，其在职仅八个月。

Yukio Hatoyama had been in power for just eight months

He was forced out after breaking an election pledge to move an unpopular US military base away from the southern island of Okinawa（冲绳县） .

The move comes as his Democratic Party of Japan (DJP) struggles to revive（苏醒，复兴） its chances in an election due in July.

The centre-left DPJ's election landslide¹ last year ended half a century of conservative rule in Japan.

But wrangling²（争吵，争辩） over the base distracted attention from their broader aims - pursuing a more equal alliance（联盟，联合） with the US, a bigger welfare state, and to seize control of policy-making from the bureaucracy（官僚主义） , says the BBC's Roland Buerk in Tokyo.

Mr Hatoyama, 63, was Japan's fourth prime minister in four years.

Broken promise

Until Tuesday night, Mr Hatoyama had insisted he would stay on while intermittently³（间歇地） holding talks with key members of his Democratic Party of Japan.

But he announced his resignation at a special meeting of DJP lawmakers on Wednesday.

He said he had asked Ichiro Ozawa, the party's secretary general - known as the "Shadow Shogun" for his power behind the scenes - to go too.

Mr Hatoyama had been under pressure to quit since last week when it was confirmed that an unpopular US base would be staying on Okinawa.

For months he had searched fruitlessly（无益地，徒劳地） for an alternative location to fulfil a pledge to move it off the island or even out of Japan altogether, our correspondent says.

When he failed his governing coalition⁴ split.

Members of his party had feared with him at the top they would be trounced（痛打，严斥） in mid-term elections to the upper house of parliament expected next month, our correspondent says.

The DPJ's next leader will have to take the party into mid-term elections to the upper house of parliament expected next month.

Possible successors include Deputy Prime Minister and Finance Minister Naoto Kan, with Foreign Minister Katsuya Okada and Transport Minister Seiji Maehara also seen as possible contenders（竞争者） .