German Chancellor Angela Merkel called Monday for answers over "grave" US spying accusations which she said were testing transatlantic ties, including fledgling trade talks.

German Chancellor Angela Merkel called Monday for answers over "grave" US spying accusations which she said were testing transatlantic ties, including fledgling trade talks.

Ahead of a special debate on snooping by US intelligence on German soil which included the suspected tapping of her mobile phone, Merkel addressed the US espionage claims at the start of a speech to parliament.

"The transatlantic relationship and therefore also the negotiations for a free-trade agreement are presently without doubt being put to the test by the remaining accusations against the US and the million-fold collection of data," Merkel told the Bundestag lower house.

"The accusations are grave. They must be explained and, more important still for the future, new trust must be built," she said to applause.

Merkel, who went on to speak about EU partnerships with Eastern European nations, did not directly mention the surveillance of her phone.

But she stressed that the relationship with the United States was of "paramount" importance for Germany and Europe, and the "common experiences, values and interests" shared by Berlin and Washington.

With US President Barack Obama's June visit to Berlin still fresh in many minds, lawmakers called a special parliamentary debate on the revelations that have put Washington in the firing line and strained diplomatic ties, also clouding EU-US talks on what would be the world's biggest free-trade accord.

Interior Minister Hans-Peter Friedrich criticized Washington's intelligence policy since the first revelations from leaked US National Security Agency (NSA) documents came to light. "The silence leads to there being all sorts of conspiracy theories," he lamented.