Nine weeks before elections, German Chancellor Angela Merkel weathered a media grilling on Friday on US online surveillance and her government's role in it, insisting she was still waiting for answers from Washington.

Merkel remains the frontrunner for the September 22 vote, and a new poll suggests the snooping affair is not yet a major election issue but the opposition hopes this will change while the media is turning increasingly hostile.

Pressed on the US National Security Agency's PRISM programme for most of a 100-minute annual summer press conference, Merkel maintained she learnt of it through media reports, was unfamiliar with the details and urged patience.