The United States National Security Agency (NSA) asked the Japanese government in 2011 to help it monitor fibre-optic cables carrying personal phone calls and email data through Japan to the Asia-Pacific region, reported the Kyodo news agency.
The U.S. intention was to spy on China, as most of the cables connecting China to the rest of the region run through Japan.
But Japan refused, citing legal restrictions and a shortage of personnel, according to reports.
Japan is the latest country, after France, Germany and Spain, to become involved in the U.S. spying revelations leaked by fugitive Edward Snowden, a former NSA contractor who is wanted in the U.S. on espionage charges.
The Spanish newspapers El Pais and El Mundo reported that the U.S. spied on over 60 million phone calls in the country in one month’s time.
France and Germany have already summoned the respective U.S. ambassadors to register their dissent against the NSA surveillance practices.
British media reported last week that the NSA had monitored the phones of 35 world leaders, with the source again being Snowden.
An EU parliamentary delegation has been sent to Washington to convey its concerns in a meeting with officials there.
British MEP Claude Moraes, head of the delegation, said it was the scale of the NSA’s surveillance that was worrying.
“The headline news, that 35 leaders had their phones tapped, is not the real crux of the issue,” he said.
“It really is the El Mundo type story, that millions of citizens of countries… had their landlines and other communications tapped. So it’s about mass surveillance. It’s about scale and proportionality.”
He said the European mission’s priority is to discuss the impact of American spying on EU citizens’ fundamental right to privacy.
With every new allegation, demands in Europe are growing for explanations and a change in culture.
EU leaders have said that distrust over U.S. spying could hurt the fight against terrorism.