By Charles Scanlon BBC Tokyo Correspondent

A prominent Japanese politician has resigned from the ruling Liberal Democratic Party in a scandal that has damaged the administration of Prime Minister Junichiro Koizumi.

The Japanese call it the iron triangle - the secretive collusion between politicians, bureaucrats and businessmen

Muneo Suzuki agreed to leave the party after revelations that he wielded enormous influence behind the scenes over foreign ministry bureaucrats.

He is alleged to have rigged bids for overseas construction projects to suit his corporate backers.

The Japanese call it the iron triangle - the secretive collusion between politicians, bureaucrats and businessmen that dominates public life.

Secret deals

In recent weeks, they have watched with fascination as the murky back-room dealings at the foreign ministry have been exposed for all to see.

Muneo Suzuki is a back-bench MP from the northern island of Hokkaido. He was also a prodigious fundraiser and a key player in the ruling party's richest and most powerful faction.

The incident has damaged Junichiro Koizumi's reputation

He used his influence to maximum effect at the foreign ministry, allegedly ensuring overseas contracts went to his friends in the construction industry.

A dam project in Kenya and building work on Russian islands claimed by Japan have come in for particular scrutiny.

Mr Suzuki is also alleged to have had a say in the accreditation of diplomats, and on one occasion, to have kicked and hit a senior ministry official in a dispute over policy.

He has finally been forced to resign from the party. In a tearful speech, he apologised for causing trouble, but denied he had done anything illegal.

The case has been extremely damaging for Japan's prime minister, Junichiro Koizumi.

He sacked his popular foreign minister, Makiko Tanaka, in January after she became entangled in a dispute with Mr Suzuki.

Many are now asking why she had to go. They see her as the only minister who was serious about cleaning out endemic corruption in the system.