Toshikatsu Matsuoka was found unconscious in a residence for lawmakers and rushed to hospital where he died.

 News reports said the 62-year-old hanged himself while in his pyjamas using a dog leash attached to his living room door.

 His death is a blow to Prime Minister Shinzo Abe and his government, whose approval ratings have plummeted amid the allegations. He had strongly defended Matsuoka, a political insider who had helped him rise up the ruling party.

 "It is extremely unfortunate and I am overwhelmed with regret. I want to pray for the rest of his soul," a visibly shaken premier told reporters after seeing Matsuoka's body at the hospital.

 "I had an opportunity to see his face. He had a very peaceful face," Abe added.

 "In expanding Japan's exports, he used his expertise and did all he could. It is extremely unfortunate as I had high expectations of him," the premier said, noting Matsuoka's role in resuming rice sales to China.

 Abe declined to elaborate on the political impact of the suicide, although he acknowledged Matsuoka "was under fierce questioning in parliament."

 Matsuoka had become embroiled in a scandal involving political funding and bid-rigging.

 Two committees set up to support his electoral campaigns allegedly received money from a group of businesses which then made bids for public works projects doled out by the government, according to media reports.

 Prosecutors last week arrested two senior officials of the government body involved in the scandal, which involved contracts for building forest roads in Matsuoka's home district.

 "I painfully feel the responsibility as a supervisory minister," Matsuoka had told reporters Friday of the arrests. "I believe it is my responsibility not to let anything like this occur again."

 More than 30,000 people kill themselves every year in Japan, making the nation's suicide rate among the highest in the world.

 Matsuoka, a career agriculture ministry bureaucrat turned politician, has also come under fire for allegedly claiming bills of up to 29 million yen (240,000 dollars) over five years to pay for utilities at his rent-free office.

 While he is not legally required to publicly report such expenses, the opposition has demanded he explain the spending, as the building is managed by the government.

 The opposition had been expected to press him on the issue in parliament later Monday.

 Earlier Monday, newspaper opinion polls said the scandal was a factor that has caused the Abe government's approval ratings to tumble.

 Support for the cabinet's performance fell to 32 per cent, down 11 points from April and the lowest since Abe came to power in September, according to the Mainichi Shimbun newspaper.

 It raises question marks over earlier assumptions that Abe would coast to a victory in national elections due in July.

 At 52 Japan's youngest post-World War II prime minister, he has tried hard to shake off perceptions that he cannot control the old guard of his party, which has ruled Japan almost continuously since 1955.

 Two of Abe's top aides resigned late last year in separate scandals, while other ministers have made embarrassing gaffes.

Agence France Presse