Survivors and relatives of victims of Japan's 1938-1942 bombings of Chongqing, China, will file a damages suit against the Japanese government later this month, their lawyers said.
About 40 people will demand 10 million yen each in damages, arguing the repeated attacks violated international humanitarian law.
Japan ratified the Hague Convention in 1911, which banned attacks on unarmed cities, the lawyers said.
"Asian people have questioned whether the Japanese government really feels remorse over its wartime aggression, as it has only presented an ambivalent attitude about it," said Keiichiro Ichinose, a lawyer representing the group. "The suit is significant in that it questions the legality of the Chongqing bombings."
The bombings of Chongqing are said to have been aimed at taking down the government led by Chiang Kai-shek by bombing the capital city at the time. A recent study by a Chinese group shows about 23,600 people died and 31,000 were wounded in the attacks.
Gao Yuan, 77, who will head the plaintiff group, lost a sister in July 1940. Others, mostly in their 70s and 80s, either lost family members or have been left with disabilities due to wounds sustained in the bombings.
The victims and their families said Japan indiscriminately attacked the former capital to make residents lose their will to fight.
A similar suit is scheduled to follow, pushing the total number of plaintiffs to about 100.