Wikileaks releases documents reportedly showing US spied on Japan for years

The Wikileaks website has published what it claims are leaked documents from the US National Security Agency showing that America spied on Japan, one of its closest allies in the Asia Pacific.

The whistle-blowing website also claimed the US shared some of its intelligence with Australia.

The intercepts exposing US National Security Agency activities follow other documents released by the whistleblower group that revealed spying on allies including Germany and France, straining relations.

Wikileaks has published five documents, four of which are marked "top secret" - which purport to reveal details of the Japanese government's positions and tactics on climate change and trade negotiations from 2007 to 2009.

The website also published a list of claimed US surveillance targets in Japan that included Japanese politicians, its top central banker and major firms.

One document on Japan's climate strategy for the 2008 G8 summit, is marked for sharing with Australia and other allies Britain, Canada, and New Zealand.

"In these documents we see the Japanese government worrying in private about how much or how little to tell the United States, in order to prevent undermining of its climate change proposal or its diplomatic relationship," WikiLeaks editor-in-chief Julian Assange said in a statement.

"And yet we now know that the United States heard everything and read everything, and was passing around the deliberations of Japanese leadership to Australia, Canada, New Zealand and the UK."

The US won't comment on the veracity of the documents, and Tokyo did not immediately react to the revelations.