The plan to legalize casino gambling has likely been delayed again, a senior Komeito official said Monday, dealing a further political blow to Prime Minister Shinzo Abe.

Casino operators such as Las Vegas Sands, Genting Singapore, MGM Resorts and Melco Crown Entertainment are waiting in the wings as potential investors in what analysts say is one of the world's biggest untapped markets, worth trillions of yen a year.

But the Diet is unlikely to have enough time to pass the controversial bill during its current session, the official from the ruling coalition said.

"The hurdle is quite high for both Lower and Upper houses to enact it" during the current session, which ends Nov. 30, said Keiichi Ishii, policy chief of Komeito, the junior partner in Abe's coalition.

Abe, who wants Japan's first casino open in time for the 2020 Tokyo Olympics, saw two Cabinet ministers resign Monday, moves that could complicate tough decisions on key policies.

But Ishii said there is concern among some Komeito members over the effects of gambling on society.

Pro-casino lawmakers last week agreed to revise the bill by mentioning the need for limits on Japanese nationals' entry to casinos, bowing to pressure from opponents who threatened to block the legalization unless issues such as gambling addiction are addressed.