The leaders came together on the eve of official campaigning

Campaigning for the 11 September poll officially begins on Tuesday.

The snap poll was called by Mr Koizumi earlier this month, after parliament rejected his plans to privatise the country's massive postal system.

Mr Koizumi says the poll will give the public a chance to give their own opinion on his postal reforms.

He has made the bill a key part of his economic agenda - staking his reputation on the policy.

Proponents of the reforms say they are urgently needed to put the postal service's huge deposits into the hands of private investors and re-ignite the economy.

But opponents fear the changes would lead to a poorer postal service and the loss of many thousands of jobs.

Japan Post has about 25,000 post offices nationwide, which sell savings and insurance products as well as offering regular postal services.

'Main focus'

A relaxed-looking Mr Koizumi - along with his coalition partner, New Komeito leader Takenori Kanzaki - lined up against the heads of four other parties for Monday's debate.

The postal reforms formed a major party of the debate

Mr Koizumi used the two-hour event to remind voters why he called the election.

He portrayed himself as a reformer, challenging his opponents to make good on promises to change the way Japan does business.

"Privatising the post office is the most important policy of my government," he said. "It's the main focus of my reforms."

"I want to ask the Japanese people what they really think," Mr Koizumi added.

His main opponent, Katsuya Okada, the leader of the Democratic Party of Japan, has been put in a difficult position, according to the BBC correspondent in Tokyo, Chris Hogg.

By opposing the postal privatisation bills, he has allowed Mr Koizumi to paint his party as anti-reform.

During the debate Mr Okada attacked the detail of the prime minister's plans, and said a number of public sector reforms were necessary which only a change in government could achieve.

"We want to stress the importance of pension and childcare issues... The Koizumi government cannot achieve these reforms," he said.

The wide-ranging discussion also touched on Japan's continuing deployment of troops to Iraq for non-combat operations.