The US spied on senior Japanese politicians, its top central banker and major companies including conglomerate Mitsubishi, according to documents released Friday by WikiLeaks, which published a list of at least 35 targets.
The latest claim of US National Security Agency espionage follows other documents that showed snooping on allies including Germany and France.
There is no specific mention of wiretapping Prime Minister Shinzo Abe but senior members of his government, including Trade Minister Yoichi Miyazawa and Bank of Japan governor Haruhiko Kuroda were targets of the bugging by US intelligence, WikiLeaks said.
Japan is one of Washington's key allies in the Asia-Pacific region and they regularly consult on defence, economic and trade issues.
The spying goes back at least as far as Abe's brief first term, which began in 2006, WikiLeaks said. Abe swept to power again in late 2012.
"The reports demonstrate the depth of US surveillance of the Japanese government, indicating that intelligence was gathered and processed from numerous Japanese government ministries and offices," it said.
"The documents demonstrate intimate knowledge of internal Japanese deliberations" on trade issues, nuclear and climate change policy, among others, it added.
There was no immediate reaction from Tokyo on the documents released by WikiLeaks.