It spied on Japanese technical development plans and climate change policy.
WikiLeaks has published new documents exposing National Security Agency (NSA) spying activity on Japanese conglomerates, government officials, ministries, and companies between September 2006 and September 2007.
On Friday, WikiLeaks released "Target Tokyo", which listed 35 telephone numbers that were targeted by the US spy agency.
According to the documents, marked "top secret", the US was allegedly snooping on the conversations that were taking place between the Japanese government ministries and offices.
One of the reports was marked "REL TO USA, AUS, CAN, GBR, NZL", which means that US was authorised to release its findings to intelligence partners belonging to Australia, Canada, Great Britain and New Zealand.
WikiLeaks said that NSA spied on the "Government VIP Line" to snoop on Chief Cabinet Secretary Yoshihide, it also listened to conversations made by officials of Japanese Central Bank.
It also said to have tapped the home phone number of at least one Central Bank official and spied on Trade and Industry Yoichi Miyazawa and the Natural Gas Division of Mitsubishi.
The leaked documents claimed that the programme was to gain knowledge of internal Japanese discussions about Japanese technical development plans, climate change policy, nuclear and energy policy and carbon emissions schemes.
It also listened to conversations regarding Japanese technical development plans, climate change policy, nuclear and energy policy and carbon emissions schemes, along with correspondence with international bodies, and got hold of content of a confidential Prime Ministerial briefing that took place at Shinzo Abe’s official residence.
WikiLeaks Investigations editor Sarah Harrison said: "Today’s publication shows us that the US government targeted sensitive Japanese industry and climate change policy.
"Would the effectiveness of Japan’s industry and climate change proposals be different today if its communications had been protected?"