Germany is asking British cabinet ministers for information about accusations of mass surveillance by British intelligence.
Justice minister Sabine Leutheusser-Schnarrenberger has asked if the surveillance by GCHQ was legal and if Germans were targeted.
Previously she said the gathering of vast amounts of global data sounded like a "Hollywood nightmare".
The Foreign Office said it does not comment on intelligence matters. Foreign Secretary William Hague told parliament two weeks ago, though, that British security agencies uphold the law at all times.
Information leaked by Edward Snowden to The Guardian suggests that GCHQ is able to tap into and store internet data from fibre optic cables for 30 days in an operation called Tempora.
The GCHQ is also said to have accessed information about British citizens from the Prism monitoring programme run by the US National Security Agency.
The GCHQ has insisted it is "scrupulous" in complying with the law.
Ms Leutheusser-Schnarrenberger's request for more information from the British government came after German Chancellor Angela Merkel voiced unease at the accusations in The Guardian.