Resignation of Keishu Tanaka adds to pressure on prime minister Yoshihiko Noda to call an early general election

Japan's prime minister, Yoshihiko Noda, has come under renewed pressure to call an early general election following his justice minister's resignation over past connections to organised crime.

Keishu Tanaka, who was appointed just three weeks ago in a cabinet reshuffle intended to boost support for Noda, stepped down on Tuesday after a weekly magazine exposed his previous contacts with members of the yakuza, Japan's influential crime syndicates.

The government cited poor health as the cause of Tanaka's resignation after the 74-year-old was admitted to hospital last Friday with chest pains, high blood pressure and an irregular heartbeat.

The chief cabinet secretary, Osamu Fujimura, told reporters: "After having a health examination, it was determined that with his symptoms, it was necessary to rest. It is regrettable, but I have accepted the resignation."

But revelations that Tanaka, who is responsible for the country's criminal justice system, had acted as a matchmaker at the wedding of a senior gang member, and attended a party organised by the same gang's leader 30 years ago fuelled speculation that he would step down.

Soon after becoming justice minister, Tanaka admitted receiving 420,000 yen [£3,200] from a foreign-owned company between 2006 and 2009. Japan's electoral laws forbid politicians from knowingly accepting funds from foreign sources. His office said it had returned the money.

Tanaka claimed he had been unaware of the groom's connections when he agreed to act as nakodo – a ceremonial role in Japanese weddings – and had no idea the party was being hosted by a yakuza boss.

His resignation has attracted fresh criticism of Noda's judgment following the resignation in September 2011 of his trade and industry minister, Yoshio Hachiro, who had described an area in Fukushima, scene of last year's nuclear disaster, as a "ghost town" and joked about radioactive contamination.

Shigeru Ishiba, secretary general of the main opposition Liberal Democratic party [LDP], told reporters shortly before Tanaka's resignation: "Even if he quits, that won't be the end of it."

Noda, though, has so far resisted calls for an early general election, with polls suggesting his party would lose just three years after it swept to power in a landslide.

"The resignation is likely to further weaken Noda's support within his party. Obviously, it will become more difficult for him to exert leadership," Mikitaka Masuyama, a professor at the National Graduate Institute for Policy Studies, told Reuters.

"But it is uncertain whether this could be a trigger for an early election. Given falling public support for the government, there is no benefit in him dissolving parliament and calling snap election at the moment."

Noda also faces criticism of his handling of the economy and a controversial doubling of sales tax to 10% over the next three years. In return for their support for the tax rise, the LDP had demanded that Noda call an election by the end of the year.

The LDP and other opposition parties control the upper house, enabling them to block key legislation.

Noda, whose government's support rating slipped below 20% for the first time this week, promised to hold an election soon but has yet to specify when. His refusal to name a date is expected to lead to further deadlock as parliament prepares to debate a key deficit-bond issuance bill.