Former Prime Minister Yasuhiro Nakasone said Tuesday that Japan needs to consider developing nuclear weapons, taking into account the presence of nearby nuclear states and the uncertain future of the alliance with the United States.

"There is a need to also study the issue of nuclear weapons," Nakasone said during a news conference to release a report by the Institute for International Policy Studies, an independent research institute he chairs, that proposes considering the nuclear option.

"There are countries with nuclear weapons in Japan's vicinity," he said. "We are currently dependent on U.S. nuclear weapons (as a deterrent), but it is not necessarily known whether the U.S. attitude will continue."

Nakasone conceded that the nuclear option should come after the country makes efforts to reinforce the global nonproliferation regime, saying, "The first priority is to keep being a nuclear-free state, and the second is to reinforce the system under the Nuclear Nonproliferation Treaty."

Prime minister from 1982 to 1987, Nakasone retired from the Diet in 2003.

He has continued making political proposals from the institute, including one in January on revising the Constitution, which stirred up debate in the ruling Liberal Democratic Party.

The institute's report, titled "An Image of Japan in the 21st Century," says the country should consider the nuclear option while at the same time maintaining its nonnuclear status and endeavoring to strengthen the nonproliferation regime.

The paper says if Japan decides to get nuclear weapons, the pacifist Constitution must be amended.