German Chancellor Angela Merkel said Monday she was surprised by revelations of mass US online surveillance and that she would call for "transparency" on its scope in talks with President Barack Obama this week.
Merkel confirmed in an interview with commercial broadcaster RTL that she would discuss with Obama an issue which has caused deep unease in Germany, where memories of the East German Stasi's spying on citizens are still raw.
"I will call for more transparency," said Merkel, who grew up in the communist East.
She was speaking ahead of a G8 summit opening in Northern Ireland on Monday and talks with Obama in Berlin on Wednesday.
She said Germans wanted to know if their online data was being sniffed out by the US National Security Agency (NSA).
"We have to be clear -- what is being used, what is not being used," she said.
Merkel said that she was "certainly surprised" by the reports about the so-called PRISM programme, while noting that she recognised that secret services needed to address the threat of terrorism with 21st century surveillance techniques.
"However it must be proportional," she said.
The White House on Friday sought to cool German fears over its secret Internet surveillance programme, saying Obama would tell Merkel that it was purely aimed at thwarting terror attacks.
But Ben Rhodes, a US deputy national security advisor, pointedly noted that Germany had served as a staging ground for some of the hijackers who plotted the September 11, 2001 attacks.
Under the PRISM programme that came to global attention this month, the NSA can issue directives to Internet firms such as Google and Facebook to gain access to emails, online chats, pictures, files and videos uploaded by foreign users.
The European Union has expressed disquiet over the scheme and warned of "grave adverse consequences" to the rights of European citizens.