Citizens' groups held protests Thursday against security bills the Cabinet of Prime Minister Shinzo Abe was set to approve later in the day, saying legislation to expand the scope of Self-Defense Forces operations overseas would undermine the pacifist Constitution.

Some 500 protesters gathered in front of the prime minister's office in the morning, holding placards and calling for the bills to be scrapped.

"This will be security legislation that enables the SDF to engage in warfare overseas," said 68-year-old Shingo Fukuyama, one of the protest organizers.

"If a war starts, it will be our generation that will be dispatched," said a 23-year-old graduate school student in Tokyo who was at the demonstration. "I cannot tolerate this."

If passed by the Diet, the legislation would mark a drastic shift in the country's security policies, loosening restrictions on where the SDF can operate. It would also allow the SDF to come to the aid defend Japan's main ally, the United States, and other friendly countries under certain conditions for the first time since World War II.

"Abe's government is downplaying the Constitution, and it makes me worry that Japan could end up in a shambles," said a 66-year-old female participant who declined to be named.

The Cabinet made a contentious decision last July to reinterpret the Constitution to allow the country to exercise the right to collective self-defense, or to come the aid of friendly nations under attack even if Japan itself is not, under certain conditions. The move has prompted scholars to criticize the reinterpretation as running counter to the war-renouncing Constitution.