US President Barack Obama has apologised to Tokyo after WikiLeaks claimed Washington had spied on Japanese politicians.
Obama held a telephone conversation with Prime Minister Shinzo Abe on Wednesday morning (local time), spokesman Yoshihide Suga says, adding the pair agreed to work together on global economic issues in the wake of a stock market meltdown sparked by fears over China.
"President Obama said he was very sorry ... as the case caused a big debate in Japan," Suga told a news conference, without confirming the spying claims.
He added that Abe reiterated his "serious concern" over the case.
"Prime Minister Abe told [Obama] that, if the Japanese people concerned were subject to these activities, it would risk jeopardising trusting relations between allies," Suga said.
In an earlier conversation with US Vice President Joe Biden, Abe voiced similar concerns if the spying claims were confirmed.
Last month, WikiLeaks said it had intercepts revealing years-long espionage by the US National Security Agency (NSA) on Japanese officials and major companies.
Tokyo's response has been widely seen as muted compared to the anger expressed in France and Germany following similar NSA spying allegations.
Japan is one of Washington's key allies in the Asia-Pacific region and they regularly consult on defence, economic and trade issues.