Japan sought answers from the United States on Tuesday over claims it had bugged its key Asian ally, as the list of embarrassing revelations from fugitive intelligence specialist Edward Snowden grows longer.
Chief Cabinet Secretary Yoshihide Suga said Tokyo was waiting to hear from the US if the allegations of a bug in its Washington embassy were true.
"I refrain from commenting on details of diplomatic dialogue, but obviously we have a great interest in this matter," Suga told reporters "We are currently asking for appropriate confirmation."
The demand comes as anger continues to grow in Europe over claims that the US had been spying on several European countries, including Germany, and the European Union.
They also come as Snowden, who is still holed up in a Moscow airport, broke his 10-day silence and accused Washington of pressuring foreign capitals to reject his asylum applications.
He has asked a total of 21 countries to consider his request, it was revealed Tuesday.
Britain's Guardian newspaper at the weekend reported top-secret US National Security Agency documents leaked by Snowden show that US intelligence services were spying on 38 embassies and diplomatic missions of its allies including the European Union and Japan.
The revelation sparked fury in European capitals, with French President Francois Hollande warning the row threatened to jeopardise talks on a free trade deal between the EU and the US.
The German government expressed its "astonishment" and "great displeasure" at the claims.
US Secretary of State John Kerry's insistence Monday that information-gathering was "not unusual" did little to stem the anger.
Japan's more moderate response may reflect its greater dependence on the US, which is treaty-bound to protect it from military attack.
Under the administration of Prime Minister Shinzo Abe, Japan is trying to re-heat a relationship that had gone slightly cold under the three-year stewardship of the now-opposition Democratic Party of Japan.