TOKYO - THE candidate for Japanese Prime Minister Taro Aso's ruling coalition has suffered a defeat in a key regional poll at the weekend, officials said Monday, dealing a fresh blow to the embattled leader.

Mr Heita Kawakatsu, 60, backed by the main opposition Democratic Party of Japan (DPJ), won Sunday's neck-and-neck contest for a governor's post in central Shizuoka prefecture with 728,706 votes, local election officials said.

Ms Yukiko Sakamoto, also 60, supported by Aso's Liberal Democratic Party (LDP) and its junior coalition partner, won 713,654 votes with all ballots counted, officials said.

It was one of two polls that will likely influence Mr Aso's decision on the timing for a general election he must call by September. The other is the Tokyo assembly election on July 12.

'It was extremely regrettable,' LDP secretary general Hiroyuki Hosoda told reporters. 'It was a very close contest. Now, we have to work hard for the general elections.' Ms Sakamoto's defeat, which came after Mr Aso's third mayoral election loss last month since April, will be a serious setback for the premier, whose poll ratings have plunged below 20 percent.

Public support for Aso's cabinet fell to 17.7 per cent from 23.5 per cent last month, according to a poll released early on Monday by Nippon Television Network, which questioned 1,088 eligible voters across the nation at the weekend.

'We will carry this victory over to the Tokyo assembly election,' Mr Katsuya Okada, secretary general of the opposition party, said in a statement. 'We will then achieve a change of power at the general elections.' The premier, in office less than a year, already faces mounting pressure from within his party to quit the leadership so a new face can lead it into the general election.

Many pundits predict that the LDP, having lost the upper house in 2007, is likely also to lose its large majority in the powerful lower house to the DPJ. -- AFP