Berlin - German Chancellor Angela Merkel may well have known about sweeping US and British online surveillance activities, the chief of the opposition Social Democrats charged in an election-year attack on Monday.
"The chancellor's reaction raises the suspicion that she was aware of the spying ... at least in principle," Sigmar Gabriel wrote in a commentary for Tuesday's edition of the Frankfurter Allgemeine Zeitung daily.
Gabriel, leader of the Social Democratic Party (SPD), challenged the conservative leader to "say whether she knew about it and tolerated it", said excerpts of his article pre-released on Monday.
Merkel will seek a third term in a 22 September election, and the claims by fugitive leaker Edward Snowden of mass spying by the US National Security Agency and British secret service have become a hot political issue.
Merkel during a visit by US President Barack Obama last month called for balance between security and privacy concerns.
On Monday, her spokesperson said she would seek another talk with Obama over new spy claims since, including the bugging of EU facilities, saying sternly that "trust must be restored" and that "this is not the Cold War anymore".
Merkel's conservative coalition government with the pro-business Free Democrats is defending a lead over their rivals, the SPD, whose top candidate is Peer Steinbrueck, and their preferred allies, the Greens party.
Gabriel also called for the European Commission to start legal proceedings against EU member Britain because "spying on millions of EU citizens surely contravenes the European treaties in word and spirit".
In further comments, Gabriel attacked what he said was the merging of private sector and state surveillance and Silicon Valley's role in the emergence of an "intelligence surveillance state", charging that "with allies like Google or Facebook, there is now little that's inconceivable".