Image caption Mr Tanaka's resignation is seen as another setback to PM Noda

Japan's justice minister has resigned weeks after taking office citing ill health, amid a scandal over alleged ties to an organised crime group.

Keishu Tanaka, 74, only assumed the post on 1 October. He was hospitalised on Friday for chest pains.

Calls for him to step down mounted amid questions over political funding and his role in a gangster wedding.

His resignation is another setback for Prime Minister Yoshihiko Noda, whose poll figures are plummeting.

Mr Tanaka is the second minister to step down in the year since he took office.

In September 2011 Yoshio Hachiro, the newly-appointed trade minister, resigned after calling the area around the tsunami-hit Fukushima nuclear plant a "town of death".

'Matchmaker'

Japan's top government spokesman, Chief Cabinet Secretary Osamu Fujimura, said Mr Tanaka had stepped down due to ill health.

"After having a health examination, it was determined that with his symptoms it was necessary to rest. And while it is regrettable, I have accepted the resignation," Mr Fujimura said.

Mr Tanaka had been justice minister for just over three weeks, following a cabinet reshuffle by Mr Noda aimed at revitalising his cabinet in the face of poor poll numbers.

He has admitted he acted as a matchmaker - a ceremonial role - at a gangster's wedding and attended a party thrown by a "yakuza" crime group boss.

But he said he was not aware of either individual's yakuza links at the time of the event, which took place 30 years ago.

He also admitted his office had accepted donations from a foreigner-run company between 2006-2009 - banned under political funding law. His office says it has returned the money.

Earlier this week, approval ratings for the Noda government slipped below 20% for the first time, Japanese media reported.

The prime minister has promised to call an election - due by the end of next year - soon, but it is not clear yet when this will happen.