Tokyo is considering suspending or reducing its financial contribution to UNESCO in response to the U.N. body's acceptance, through closed-door processes, of Beijing's documents on the 1937 Nanking Massacre, Chief Cabinet Secretary Yoshihide Suga said Tuesday.

On Friday, UNESCO announced that it had registered what China claims are historical documents on the Nanking Massacre, also known as the Rape of Nanking, in its Memory of the World program.

Suga claimed the process of registration happened without verification by third-party experts, lacked "transparency" and violated the political "neutrality" of UNESCO.