'There is a possibility that a general election will be held in May or June,' Mr Ichiro Ozawa, head of the main opposition Democratic Party, said at a seminar.

'In any case, we will definitely face a general election by the end of the year and we must win,' he added.

The current term of the House of Representatives, the more powerful lower house, expires in September next year.

The opposition has been increasing its calls for an early election since winning a majority in the upper house in July last year.

Mr Fukuda, who marked six months in office last week, has suffered a sharp drop in popularity amid political deadlock over key legislation, including a gasoline tax and the appointment of a new central bank chief.

But at the same time, recent polls suggest the opposition has failed to take full advantage of the fall in government support.

Mr Fukuda apologised to voters on Monday for his failure to persuade the opposition to accept a proposal to keep a special tax on petrol to raise funds mainly for road projects.

Mr Fukuda, whose Liberal Democratic Party has ruled Japan almost continuously for half a century, has resisted opposition calls for an early election as he prepares to host a summit of the Group of Eight major economies in July. -- AFP