TOKYO, Japan (AFP) — Japan's Prime Minister Yoshihiko Noda is facing mounting pressure following his justice minister's admission to past links with a yakuza gang, just 10 days after he was appointed.

Justice Minister Keishu Tanaka on Friday apologised that he had associated with members of an organised crime syndicate, after a tabloid magazine reported that he had been presented as top guest of a yakuza member's wedding party.

"If I had known he was a member (of a yakuza group), I would not have been there," he said, admitting that he had attended the party about 30 years ago.

"I was taken there and realised that they were members of a crime syndicate. I am sorry for having had the kind of relations," he said.

Opponents have seized the opportunity to criticise Noda's new cabinet, with some demanding the minister's resignation.

"This is unbelievable," said leading opposition Liberal Democratic Party's Yoshihide Suga in an interview with NTV broadcaster. "[The] justice minister is literally the guardian of the law. He should resign as he has admitted to it."

Like the Italian mafia or Chinese triads, the yakuza engage in activities from gambling, drugs and prostitution to loan-sharking, protection rackets, white-collar crime and business conducted through front companies.

The gangs, which are not illegal, have historically been tolerated by the authorities, although there are periodic clampdowns on some of their less savoury activities.

Tanaka, who said he has not associated with the yakuza members since the wedding, expressed his intention to stay in his post as justice minister.